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AMERICAN  SCIENCE  SERIES— BRIEFER  COURSE 

THE  HUMAN  BODY 

TEXT-BOOK  OF  ^ANATOMY,  PHYSIOLOGY 
HYGIENE 


BY 


H.  NEWELL  MARTIN,  D.Sc.,  M.D.,  M.A.,  F.R.S. 

•&&- 

Formerly  Professor  of  Biology  in  the  Johns  Hopkins  University 
and  of  Physiology  in  the  Medical  Faculty  of  the  same 


FIFTH  EDITION,  REVISED 


WITH  PRACTICAL  EXERCISES 

BY 

GEORGE  WELLS   FITZ,    M.D. 

Assistant  Professor  of  Physiology  and  Hygiene  in 
Harvard  University 


M38IH 


NEW  YORK 

HENRY  HOLT   AND   COMPANY 
1902 


Copyright,  1883,  1884,  1898, 

BY 
HENRY  HOLT  &  CO. 


2l 

PREFACE   TO  THE   FIFTH   EDITION. 

THE  revision  of  this  book  was  undertaken  with  the  idea  of 
bringing  it  into  accord  with  the  later  developments  of  physi- 
ology, of  simplifying  the  treatment  of  some  parts,  of  expand- 
ing that  of  others,  and  of  enriching  the  text  with  additional 
illustrations.  Every  effort  has  been  made  to  avoid  injuring 
those  features  of  Professor  Martin's  work  which  have  made 
the  book  so  favorably  known. 

The  changes  in  the  first  nine  chapters  are  largely  verbal ; 
in  the  tenth  and  succeeding  chapters,  however,  consider- 
able alterations  and  additions  have  been  made ;  Chapter 
XX.  has  been  entirely  rewritten,  and  Chapter  XXIII.  and 
an  Appendix  on  Emergencies  have  been  added.  The  Chap- 
ter on  Narcotics,  transferred  to  the  appendix,  is  retained 
against  the  best  judgment  of  the  reviser,  who  believes  that 
the  questions  involved  are  ethical  and  not  physiological ;  it 
stands  as  Professor  Martin  wrote  it,  except  that  the  para- 
graphs on  certain  drugs  have  been  omitted. 

The  directions  for  demonstrations  and  experiments  have 
been  greatly  enlarged  and  collected  into  an  Appendix.  They 
include  the  new  requirements  in  Anatomy,  Physiology  and 
Hygiene,  for  admission  to  Harvard  College  and  the  Law- 
rence Scientific  School.  It  is  hoped  that  teachers  will 
recognize  the  importance  of  practical  work  in  physiology  as 
in  other  sciences. 

Hi 


iv  PREFACE   TO   THE  FIFTH  EDITION. 

In  accordance  with  Professor  Martin's  own  judgment,  the 
questions  at  the  foot  of  the  page  have  been  omitted. 

I  have  been  indebted  for  practical  suggestions  to  Dr. 
Margaret  B.  Wilson,  of  the  Normal  College,  New  York  City. 

G.  W.  F. 

CAMBRIDGE,  MASS., 
August,  1898. 


PREFACE  TO  THE   FIRST  EDITION. 

THIS  elementary  textbook  of  Physiology  has  been  pre- 
pared in  response  to  many  requests  for  a  textbook  framed  on 
the  same  plan  as  the  "  Human  Body,"  but  abridged  for  the 
use  of  students  younger,  or  having  less  time  to  give  to  the 
subject,  than  those  for  whom  that  book  was  designed.  This 
demand,  and  the  fact  that  a  second  edition  of  the  "  Human 
Body  ' '  was  called  for  within  twelve  months  of  its  publica- 
tion, have  shown  me  that  I  was  not  wrong  in  believing  that 
the  teachers  of  Elementary  Physiology  in  the  United  States 
were  ready  and  anxious  for  a  textbook  in  which  the  subject 
was  treated  from  a  scientific  standpoint,  and  not  presented 
merely  as  a  set  of  facts,  useful  to  know,  which  pupils  were  to 
learn  by  heart  like  the  multiplication  table. 

That  some  instruction  in  at  least  one  branch  of  Natural 
Science  should  form  a  part  of  the  regular  educational  cur- 
riculum is  now  so  generally  admitted  that  there  is  no  need  to 
insist  upon  it.  But  if  this  instruction  simply  means  teach- 
ing by  rote  certain  facts,  no  matter  how  important  these 
facts  may  be,  the  proper  function  of  Natural  Science  in  a 
system  of  education  is  missed.  Mere  training  of  the  mem- 
ory (no  unimportant  matter)  is  otherwise  sufficiently  pro- 
vided for  in  the  usual  school  and  college  course  of  study  : 
the  true  use  of  Natural  Science  in  general  education  is  differ- 


vi  PREFACE   TO    THE  FIRST  EDITION. 

ent.  It  should  prepare  the  student  in  another  way  for  the 
work  of  subsequent  daily  life,  by  training  the  observing  and 
reasoning  faculties. 

As  a  department  of  science,  modern  Physiology  is  con- 
trolled mainly  by  two  leading  generalizations — the  doctrine 
of  the  "  Conservation  of  Energy  "  and  that  of  the  "  Physio- 
logical division  of  labor."  I  have  endeavored  in  this,  as  in 
the  larger  book,  to  keep  prominent  these  leading  principles  ; 
and,  so  far  as  is  possible  in  an  elementary  book,  to  exhibit 
the  ascertained  facts  of  Physiology  as  illustrations  of  or  de- 
ductions from  them. 

The  anatomical  and  physiological  facts  which  can  be  de- 
scribed in  books  of  the  size  of  the  present  must  be  pretty 
much  the  same  in  all.  Apart  from  the  attempt  above  men- 
tioned to  make  elementary  Physiology  a  more  useful  educa- 
tional instrument  than  it  has  frequently  hitherto  been,  the 
present  volume  differs  from  most  others  of  its  grade  in  hav- 
ing, as  footnotes  or  as  appendices  to  the  chapters,  simple 
practical  directions,  assisting  a  teacher  to  demonstrate  to  his 
class  certain  fundamental  things.  The  demonstrations  and 
experiments  described  necessitate  the  infliction  of  pain  on  no 
animal,  and  require  the  death  of  no  creature  higher  than  a 
frog,  except  such  superfluous  kittens,  puppies,  and  rats  as 
would  be  killed  in  any  case,  and  usually  by  methods  much 
less  merciful  than  those  prescribed  in  the  following  pages. 
The  practical  directions  are,  for  the  most  part,  reprints  from 
a  series  of  such  which  I  drew  up  some  years  ago  for  a  class 
composed  of  Baltimore  teachers;  those  experiments  which 
require  costly  apparatus  have,  of  course,  been  omitted.  The 
interest  which  my  "Teachers'  Class"  took  in  its  work,  and 
the  good  use  its  members  subsequently  made  of  it,  have  en- 
couraged me  to  believe  that  others  might  be  glad  of  a  few 


PREFACE   TO   THE  FIRST  EDITION.  vii 

hints  as  to  things  suitable  to  show  to  young  students  of 
Physiology. 

It  may  be  well  to  anticipate  a  possible  objection.  A  few 
persons,  some  of  them  worthy  of  respect,  assert  that  no  ex- 
periments on  an  animal  can  be  shown  to  a  class  without 
hardening  the  hearts  of  operator  and  spectators ;  even  when, 
in  accordance  with  the  directions  given  in  the  following 

•x 

pages,  the  animal  is  anaesthetized  and  while  in  that  condition 
is  killed  or  its  brain  destroyed.  This,  from  an  experience  of 
more  than  fifteen  years  in  the  teaching  of  practical  physi- 
ology, I  know  to  be  not  so.  So  far  as  the  experiments  de- 
scribed in  the  present  book  are  concerned,  their  effect  is  most 
certainly  humanizing.  Young  people  are  apt  to  be,  not  cal- 
lous, but  thoughtless  as  to  the  infliction  of  pain.  When  they 
see  their  teacher  take  trouble  to  kill  even  a  frog  painlessly, 
they  have  brought  to  their  attention  in  a  way  sure  to  impress 
them,  the  fact  that  the  susceptibility  of  the  lower  animals  to 
pain  is  a  reality,  and  its  infliction  something  to  be  avoided 
whenever  possible. 

As  the  question  of  size  is  no  unimportant  one  in  relation 
to  textbooks  designed  for  junior  students  with  many  other 
subjects  to  learn,  I  may  be  permitted  to  say  that  though  this 
volume  contains  more  pages  than  most  of  those  with  which  it 
will  have  to  compete,  I  believe  it  is  not  really  larger.  The 
extra  pages  are  due,  in  part  to  the  above-mentioned  appen- 
dices to  the  chapters,  and  in  part  to  the  great  number  and 
large  size  of  the  figures.  My  publishers  had  on  hand  electro- 
types of  the  figures  of  the  octavo  edition,  and  have  been  able 
to  utilize  them  in  illustrating  this  briefer  one  much  better 
than  most  textbooks  of  its  scope,  without  proportionately  in- 
creasing its  price. 

If  I  had  relied  solely  on  my  own  judgment  the  questions 


vin  PREFACE   TO   THE  FIRST  EDITION. 

at  the  foot  of  each  page  would  have  been  omitted.  But  it 
was  strongly  represented  to  me  by  those  whose  opinion  I  had 
reason  to  value,  that  such  questions  were  useful  in  enabling  a 
student  to  test  whether  he  had  mastered  his  lesson,  and  that 
teachers  who  disliked  such  prearranged  questions  could  and 
would  ignore  them.  I  hope  that  the  pupils  will  use  the 
questions  and  that  their  teachers  will  not. 

Before  concluding,  I  must  express  my  sincere  thanks  to 
Miss  Frances  T.  Bauman,  who  has  given  me  the  benefit  of 
her  many  years'  experience  as  an-  eminently  successful  teacher. 
She  kindly  read  a  large  portion  of  the  manuscript,  and  gave 
me  much  advice  of  which  I  have  been  glad  to  avail  myself. 
I  have  also  to  acknowledge  my  indebtedness  to  Mr.  W.  H. 
Howell,  Fellow  of  the  Johns  Hopkins  University,  who  has 
corrected  most  of  the  proof-sheets  and  prepared  the  index. 

H.  N.  M. 

JOHNS  HOPKINS  UNIVERSITY, 
August  10,  1883. 


CONTENTS. 

CHAPTER  I. 

THE   GENERAL  STRUCTURE  AND  ARRANGEMENT  OF  THE   HUMAN   BODY. 

I'AGE 

Human  Physiology — Hygiene — Anatomy — Histology — Tissues 
— Organs — The  general  plan  on  which  the  body  is  con- 
structed— Man  is  a  vertebrate  animal — Contents  of  the  two 
chief  cavities  of  the  body— The  limbs— Man's  place  among 
vertebrates — Summary I 

CHAPTER  II. 

THE  MICROSCOPICAL   AND    CHEMICAL   COMPOSITION   OF   THE   BODY. 

What  are  the  tissues  ? — Cells  and  fibres — The  physiological  divi- 
sion of  labor  and  its  results — The  chemical  composition  of 
the  body — Albumens,  fats,  and  carbohydrates II 

CHAPTER  III. 

THE    SKELETON. 

Bone,  cartilage,  and  connective  tissue — Articulations  and  joints 
— The  bony  skeleton — Value  of  the  structural  arrangement 
of  the  spinal  column — Comparison  of  the  skeletons  of  the 
upper  and  lower  limbs — Peculiarities  of  the  human  skeleton.  17 

CHAPTER  IV. 

THE  STRUCTURE,    COMPOSITION,    AND    HYGIENE   OF  BONES. 

Gross  structure  of  bones— The  humerus — Why  many  bones  are 
hollow — Histology  of  bone— Chemical  composition  of  bone — 
Hygiene  of  the  bony  skeleton — Fractures 36 


CONTENTS. 
CHAPTER  V. 

JOINTS. 

PAGE 

Muscles  and  joints — Structure  of  the  hip  joint — Ball  and  socket 
joints — Hinge  joints — Pivot  joints — Gliding  joints — Disloca- 
tions— Sprains 46 

CHAPTER  VI. 

THE    MUSCLES. 

The  parts  of  a  muscle — The  origin  and  insertion  of  muscles — 
Varieties  of  muscles —How  muscles  are  controlled — Gross 
structure  of  a  muscle— Histology  of  muscle— Plain  muscular 
tissue — The  muscular  tissue  of  the  heart — The  chemical  com- 
position of  muscle — Beef  tea  and  meat  extracts ...  52 

CHAPTER  VII, 

MOTION   AND   LOCOMOTION. 

The  special  physiology  of  muscles — Levers  in  the  body — Pulleys 
in  the  body — Standing — Walking — Running — Hygiene  of  the 
muscles — Exercise 64 

CHAPTER  VIII. 

WHY    WE   EAT   AND    BREATHE. 

How  it  is  that  the  body  can  do  work — The  conservation  of  en- 
ergy— Illustrations — Why  we  need  food — Why  the  body  is 
warm — The  influence  of  starvation  upon  muscular  work  and 
animal  heat— Oxidations  in  the  body — The  oxygen  food  of 
the  body 74 

CHAPTER  IX. 

NUTRITION. 

The  wastes  of  the  body — Receptive  and  excretory  organs — The 
organs  and  processes  concerned  in  nutrition — Digestion — Cir- 
culation— Respiration , , , , 83 


CONTENTS.  xi 

CHAPTER  X. 

FOODS. 

PAGE 

Foods  as  tissue  formers — What  foods  must  contain— The  special 
importance  of  albuminous  foods — The  dependence  of  animals 
on  plants — Non-oxidizable  foods — Definition  of  foods — Ali- 
mentary principles — The  nutritive  value  of  various  foods — 
Alcohol— Tea  and  coffee— Cooking— The  advantages  of  a 
mixed  diet 88 

CHAPTER  XI. 

THE   DIGESTIVE  ORGANS. 

General  arrangement  of  the  alimentary  canal — Glands — The 
mouth — The  teeth — Hygiene  of  the  teeth— The  tongue — A 
furred  tongue — The  salivary  Glands — The  tonsils — The 
pharynx — The  gullet — The  stomach — Palpitation  of  the  heart 
— The  small  intestine — The  large  intestine — The  liver— The 
pancreas . .  106 

CHAPTER  XII. 

DIGESTION. 

The  object  of  digestion — Uses  of  saliva — Swallowing— The  gas- 
tric juice — Chyme — Chyle — The  pancreatic  secretion — The 
bile  and  its  uses — The  intestinal  secretions — Indigestible  sub- 
stances— Dyspepsia — Appetite — Absorption  from  the  alimen- 
tary canal — The  lymph — The  lacteals 131 

CHAPTER  XIII. 

BLOOD   AND    LYMPH. 

Why  we  need  blood— Histology  of  blood — The  blood  corpuscles 
— Haemaglobin — The  coagulation  of  blood — Uses  of  coagula- 
tion— Blood  serum — Blood  gases — Hygienic  remarks — Quan- 
tity of  blood  in  the  body— The  lymph— Dialysis— The  lym- 
phatic or  absorbent  vessels 14? 

CHAPTER  XIV. 

THE   ANATOMY   OF   THE   CIRCULATORY   ORGANS. 
The  organs  of  circulation — Functions  of  the  circulatory  parts  of 
the  system— The  pericardium  — The  heart — The  vessels  con- 


xii  CONTENTS. 

PAGE 

nected  with  the  heart — How  the  heart  is  nourished — The 
valves  of  the  heart — The  main  arteries  of  the  body — The 
properties  of  the  arteries — The  capillaries — The  veins — The 
course  of  the  blood — The  portal  circulation — Arterial  and 
venous  blood 163 

CHAPTER  XV. 

THE   WORKING   OF  THE    HEART   AND   BLOOD  VESSELS. 

The  beat  of  the  heart — Events  occurring  in  each  beat — Use  of  the 
papillary  muscles — Sounds  of  the  heart — Function  of  the  au- 
ricles— Work  done  daily  by  the  heart — Nerves  of  the  heart — 
The  pulse — Blood  flow  in  capillaries  and  veins — Why  there 
is  no  pulse  in  these  vessels — The  muscles  of  the  arteries — 
Exposure  to  cold — Bathing 180 

CHAPTER  XVI. 

THE   OBJECT  AND  THE  MECHANICS   OF  RESPIRATION. 

The  object  of  respiration — The  respiratory  apparatus — The 
trachea — Bronchitis — The  lungs — The  pleura — Pleurisy — 
Elasticity  of  the  lungs — Inspiration  and  expiration — Structure 
and  enlargement  of  thorax — Respiratory  sounds — Why  the 
lungs  fill  with  air — The  nervous  control  of  respiration — Hy- 
gienic remarks 193 

CHAPTER  XVII. 

THE   CHEMISTRY    OF   RESPIRATION    AND    VENTILATION. 

The  quantity  of  air  breathed  daily — Changes  produced  in  the  air 
by  being  breathed — Ventilation — When  breathed  air  becomes 
unwholesome — How  to  ventilate — Changes  undergone  by 
the  blood  in  the  lungs 208 

CHAPTER  XVIII. 

THE    KIDNEYS   AND   THE   SKIN. 

General  arrangement  cf  the  nitrogen-execreting  organs— Gross 
structure  of  the  kidney — Histology  of  the  kidney — The  renal 
secretion— The  skin — Hairs — Nails — The  sweat  glands— The 
sebaceous  glands — Hygiene  of  the  skin — Bathing 215 


CONTENTS.  xiii 

CHAPTER  XIX. 

WHY    WE    NEED  A    NERVOUS    SYSTEM — ITS    ANATOMY. 

PAGE 

The  harmonious  co-operation  of  the  organs  of  the  body — Co- 
ordination— Nerve  trunks  and  nerve  centres — The  brain  and 
spinal  cord  and  their  membranes — The  spinal  cord — The 
spinal  nerves — The  brain— The  cranial  nerves — The  sympa- 
thetic nervous  system — The  histology  of  nerve  centres  and 
nerve  trunks 230 

CHAPTER   XX. 

THE    GENERAL    PHYSIOLOGY    OF    THE   NERVOUS    SYSTEM. 

The  properties  of  the  nervous  system — Functions  of  nerve 
centres  and  nerve  trunks — Sensory  and  motor  nerves  — 
Classification  of  nerve  centres — Functions  of  the  cere- 
brum— Of  the  cerebellum — Reflex  nerve  centres — Auto- 
matic nerve  centres — Habits — Hygiene  of  the  brain 247 

CHAPTER    XXI. 

THE    SENSES. 

Common  sensation  and  special  senses— Hunger  and  thirst — 
The  visual  apparatus  and  its  appendages — Movements 
of  the  eyeball — The  globe  of  the  eye — The  retina — The 
blind  spot — The  iris — The  formation  of  images  on  the 
retina — Short  sight  and  long  sight — Astigmatism — Hy- 
giene of  the  eyes — Hearing — The  tympanum — The  in- 
ternal ear — Touch — The  localization  of  skin  sensations 
— The  muscular  sense — Sense  of  pain — The  temperature 
sense — Smell— Taste 263 

CHAPTER   XXII. 

VOICE    AND     SPEECH. 

The  production  of  voice — The  pitch  of  the  voice — Resonance 
— Speech — Structure  of  the  larynx — The  vocal  chords — 
Range  of  the  human  voice — Vowels — Semi-vowels — Con- 
sonants   288 


xiv  CONTENTS. 

CHAPTER  XXIII. 

GROWTH    AND    NUTRITION. 

PAGE 

Development— Segmentation — Differentiation— Classification 
of  tissues — Cell  nutrition — Trophic  nerves — General  nu- 
trition— Internal  secretion  of  glands — Spleen — Thyroid 
gland — Suprarenal  capsules — Pituitary  body — Kidney — 
Pancreas — Health — Disease — Bacteria — Immunity  from 
disease — Toxin — Antitoxin 295 

APPENDIX   A. 

EMERGENCIES. 

Gas  poisoning — Artificial  respiration — Fainting — Sunstroke 
—  Convulsions  —  Alcoholic  poisoning  —  Concussion  of 
brain — Epileptic  attacks — Apoplexy — Common  poisons 
and  their  antidotes — Bleeding — Bruises  and  sprains — 
Burns  and  scalds — Stings  of  insects — Snake  bite — Foreign 
body  in  eye — Contagious  diseases — Disinfection 307 

APPENDIX    B. 

THE  ACTION  OF  ALCOHOL  AND   TOBACCO  UPON   THE 
HUMAN   BODY. 

Introductory — Is  alcohol  a  food  ? — Composition  and  proper- 
ties of  alcohol — Alcoholic  beverages — The  direct  physio- 
logical action  of  pure  alcohol — Action  of  diluted  alcohol 
— Absorption  of  alcohol — Primary  effects  of  a  moderate 
dose  of  alcohol — Secondary  effects  of  alcohol — Minor 
diseased  conditions  produced  by  alcohol — Acute  alco- 
holic diseases — Delirium  tremens — Dipsomania — Chronic 
alcoholic  diseases — Deteriorations  of  tissue  due  to  alco- 
hol— Organs  impaired  or  destroyed  by  alcohol — Moral 
deterioration  produced  by  alcohol — Tobacco 327 

APPENDIX   C. 

DEMONSTRATIONS   AND    EXPERIMENTS. 

Bones— Muscle — Joints — Levers— Oxidation — Foods — Diges- 
tive tract — Digestion — Blood — The  heart — Heart  action 
— Respiratory  tract— Respiration — Renal  organs— Ner- 
vous system — Nerve  action — Special  senses 343 


THE   HUMAN   BODY. 

CHAPTER   I. 

THE    GENERAL  STRUCTURE  AND  ARRANGEMENT   OF  THE 
HUMAN  BODY. 

Human  Physiology  is  that  department  of  science  which 
has  for  its  object  the  discovery  and  accurate  description  of 
the  properties  and  actions  of  the  living  healthy  human  body, 
and  the  uses,  or  the  functions,  of  its  various  parts.  Physi- 
ologists endeavor  to  find  out  the  work  of  the  body  as  a 
whole,  and  of  each  of  its  parts,  and  the  conditions  under 
which  this  work  is  best  performed.  Upon  this  study  is  based 
the  science  of  Hygiene,  which  is  concerned  with  the  laws 
and  conditions  of  health. 

Anatomy. — Clearly,  to  discover  the  use  and  mode  of 
working  of  each  part  of  the  body  we  must  learn  about  the 
parts;  this  study  is  Human  Anatomy.  When  the  body  is 
examined  from  without,  it  is  seen  to  be  a  complicated  struc- 
ture with  its  head  and  neck,  trunk  and  limbs,  and  the  many 
smaller  but  distinct  parts  which  enter  into  the  formation  of  the 
larger  ones,  as  eyes,  nose,  ears,  and  mouth  to  form  the  face. 
Dissected,  its  complexity  is  seen  to  be  far  greater ;  we  then 
learn  that  it  is  made  up  of  many  hundreds  of  diverse  parts, 
each  having  its  own  form,  structure,  and  purpose,  but  all 
working  harmoniously  together  in  health. 


2  THE  HUMAN  BODY. 

Summary. — Anatomy  deals  with  the  form,  structure,  and 
connections  of  the  parts  of  the  body ;  Physiology  with  the 
uses,  or  functions,  of  the  parts,  and  the  manner  of  their 
working ;  Hygiene  with  the  conditions  of  life  which  promote 
the  health  of  the  body. 

Microscopic  Anatomy  or  Histology. — Examination  of 
the  body's  surface  shows  that  a  number  of  different  materials 
enter  into  its  formation,  such  as  hair,  nails,  skin,  and  teeth. 
By  feeling  through  the  skin,  we  find  harder  and  softer  solid 
masses  beneath  ;  by  piercing  it,  we  find  liquid  blood. 

A  closer  examination  of  any  of  its  parts,  as  the  hand,  dis- 
closes the  same  variety  of  materials.  We  see  the  skin  and 
nails;  when  the  skin  is  dissected  off  we  find  yellowish-white 
fat j  beneath  the  fat  lies  a  number  of  soft  red  masses,  the 
muscles  (which  correspond  to  the  lean  of  meat);  under  the 
muscles,  again,  are  hard,  whitish  bones  •  the  ends  of  bones 
which  form  the  joints  are  covered  by  still  another  substance, 
gristle  or  cartilage.  Finally,  binding  skin,  fat,  muscles,  and 
bone  together,  we  discover  a  tough  stringy  material,  different 
from  all,  which  is  called  connective  tissue.  If  we  take  any 
other  portion  of  the  body,  as  the  foot,  we  arrive  at  a  similar 
result ;  it,  too,  is  made  up  of  a  number  of  different  materials, 
or  tissues,  which,  though  in  this  case  identical  with  those 
found  in  the  hand,  are  arranged  in  a  different  way  so  as  to 
perform  another  function  (just  as  wood  and  nails  may  be  used 
to  build  a  house  or  a  bridge,  but  are  put  together  in  a  differ- 
ent manner  in  the  two  cases)  ;  or  we  find,  as  in  the  eye, 
some  identical  and  some  quite  different  materials. 

That  branch  of  anatomy  which  deals  with  the  arrange- 
ment of  the  materials  used  in  the  construction  of  the  parts  of 
the  body  is  called  histology,  or,  since  it  is  mainly  carried  on 
with  the  aid  of  the  microscope,  microscopic  anatomy. 


TISSUES  AND  ORGANS.  3 

Tissues. — Each  of  the  primary  building  materials  which 
can  be  recognized,  either  with  or  without  the  microscope,  as 
entering  into  the  construction  of  the  body,  is  called  a  tissue  j 
we  speak,  for  example,  of  muscular  tissue,  fatty  tissue,  bony 
tissue,  cartilaginous  tissue,  and  so  forth  ;  each  tissue  has  cer- 
tain properties  in  which  it  differs  from  all  the  rest,  and  which 
it  preserves  in  whatever  part  of  the  body  it  may  be  found. 
It  is  also,  when  examined  with  a  microscope,  characterized 
by  certain  appearances  which  are  always  the  same  for  the 
same  tissue  no  matter  where  it  is  found.  The  total  number 
of  important  tissues  is  not  great ;  the  variety  in  structure  and 
use  which  we  find  in  the  parts  of  the  body  depends  mainly 
on  the  diverse  ways  in  which  the  tissues  are  combined. 

Organs. — Each  distinct  portion  of  the  body  with  a  spe- 
cial use  or  function  is  called  an  organ  ;  thus,  the  hand  is  an 
organ  of  prehension ;  the  eye,  the  organ  of  sight ;  the  stom- 
ach, an  organ  of  digestion  ;  and  so  forth. 

Summary. — The  human  body  is  made  up  of  a  limited 
number  of  tissues  •  *  each  tissue  has  a  characteristic  appear- 
ance, by  which  it  can  be  recognized  with  the  microscope, 
and  one  or  more  distinctive  properties  which  fit  it  for  some 
special  use;  thus,  it  maybe  tough,  and  suited  for  binding 
other  parts  together ;  or  rigid,  and  adapted  to  preserve  the 
shape  of  the  body ;  or  have  the  power  of  contracting  and 
thus  of  moving  parts  to  which  its  ends  are  attached. 

*  The  various  tissues  of  the  body  will  be  considered  in  more  detail 
in  connection  with  the  study  of  the  special  organs.  The  more  important 
are  :  I.  Bony  tissue.  2.  Cartilaginous  tissue.  3.  White  fibrous  con- 
nective tissue.  4.  Yellow  elastic  tissue.  5.  Glandular  tissue,  of  which 
there  are  many  varieties.  6.  Respiratory  tissues.  7.  Fatty  tissue. 
8.  Sense  organ  or  irritable  tissues.  9.  Nerve  cell  tissue.  10.  Nerve 
fibre  tissue,  n.  Striped  muscular  tissue.  12.  Unstriped  muscular  tis- 
sue. 13.  Epidermic  and  epithelial  tissue. 


4  THE  HUMAN  BODY. 

The  tissues  are  variously  combined  to  form  the  organs  of 
the  body,  of  which  there  are  very  many,  differing  in  size; 
shape,  and  structure  ;  some  organs  contain  only  a  few  tissues  ; 
others,  a  great  many;  some  possess  only  tissues  which  are 
found  also  in  other  organs,  others  contain  one  or  more  tis- 
sues peculiar  to  themselves ;  but  wherever  an  organ  is  found, 
it  is  constructed  and  placed  with  reference  to  the  performance 
of  some  duty ;  the  organs  are  the  machines  which  are  found 
in  the  factory  represented  by  the  body,  and  the  tissues  are 
the  materials  used  in  building  the  machines ;  or,  using  an- 
other illustration,  we  may,  with  Longfellow,  compare  the 
body  to  a  dwelling-house ;  and  then  go  on  to  liken  the  tis- 
sues to  the  brick,  stone,  mortar,  wood,  iron,  and  glass  used 
in  building  it ;  and  the  organs  to  the  walls,  floors,  ceilings, 
doors,  and  windows,  which,  made  by  combining  the  primary 
building  materials  in  different  ways,  have  each  a  purpose  of 
their  own,  and  all  together  make  the  house. 

The  General  Plan  on  which  the  Body  is  Constructed.— 
When  we  desire  to  gain  a  general  idea  of  the  structural  plan 
of  any  object  we  examine,  if  possible,  sections  made  through 
it  in  different  directions  :  the  botanist  cuts  the  stem  of  the 
plant  he  is  examining  lengthwise  and  crosswise,  and  studies 
the  surfaces  thus  laid  bare ;  the  geologist,  investigating  the 
structure  of  any  portion  of  the  earth's  crust,  endeavors  to 
find  exposed  surfaces  in  canons,  in  railway  cuttings,  and  so 
forth,  where  he  may  see  the  strata  exposed  in  their  natural 
relative  positions;  so,  also,  the  best  method  of  getting  a 
good  general  idea  of  the  way  in  which  the  parts  of  the 
human  body  are  put  together  is  to  study  them  as  laid  bare  by 
cuts  made  in  different  directions. 

If  the  whole  body  is  divided  into  right  and  left  halves, 
the  cut  surface  of  the  right  half  resembles  Fig.  i.  Such  a 


GENERAL  PLAN  OF  A  BODY. 


section  shows  us,  first,  that  the  body 
essentially  consists  of  two  main 
tubes  or  cavities,  separated  by  a 
solid  bony  partition.  The  larger 
cavity,  b,  c,  known  as  the  ventral 
cavity,  lies  on  the  front  side,  and 
contains  the  organs  of  circulation, 
respiration,  and  digestion.  It  does 
not  reach  into  the  neck,  but  is  en- 
tirely confined  to  the  trunk.  The 
smaller  cavity,  a,  a' ,  is  tubular  in 
the  trunk  region,  but  passes  on 
through  the  neck,  and  widens  out 
in  the  skull ;  it  is  known  as  the 
dorsal  or  neural  cavity,  and  con- 
tains the  most  important  nervous 
organs,  i.e.  the  brain,  N' ',  and 
spinal  cord,  N.  In  the  partition 
between  the  two  cavities  is  a  stout 
bony  column,  the  back-bone  or 
spine,  e,  e,  which  is  made  up  of  a 
number  of  short  thick  bones  ar- 
ranged one  on  the  top  of  an- 
other. 

Man  is  a  Vertebrate  Animal. — 
The  presence  of  these  two  cham- 
bers with  the  solid  partition  be- 
tween them  is  a  primary  fact  in 
the  anatomy  of  the  body  ;  it  shows 
that  man  is  a  vertebrate  animal, 
thai  is,  a  back-boned  animal,  and 
belongs  to  the  same  great  group  as 


0 


FIG.  i. — Diagrammatic  longitu- 
dinal section  of  the  body,  a,  the 
neural  tube,  with  its  upper  enlarge- 
ment in  the  skull  cavity  at  a' ;  TV, 
the  spinal  cord  ;  N' ',  the  brain  ;  <?<?, 
vertebrae  forming  the  solid  parti- 
tion between  the  dorsal  and  ven- 
tral cavities  ;  b,  the  pleural,  and  tr, 
the  abdominal  division  of  the 
ventral  cavity,  separated  from  one 
another  by  the  diaphragm,  d\  i, 
the  nasal,  and  o,  the  mouth  cham- 
ber, opening  behind  into  the 
pharynx,  from  which  one  tube 
leads  to  the  lungs,  /,  and  another 
to  the  stomach, _/";  h,  the  heart;  £, 
a  kidney  ;  j,  the  sympathetic  ner- 
vous chain.  From  the  stomach,/", 
the  intestinal  tube  leads  through 
the  abdominal  cavity  to  the  pos- 
terior opening  of  the  alimentary 
canal. 


o  THE  HUMAN  BODY. 

fishes,  reptiles,  birds,  and  beasts.*  Sea  anemones,  clams,  and 
insects  are  invertebrate  animals,  and  sections  made  through 
any  of  them  from  the  head  to  the  opposite  end  would  show 
nothing  like  the  two  main  cavities  with  a  back  bone  between 
them  characteristic  of  the  vertebrates. 

Contents  of  the  Two  Chief  Cavities  of  the  Body. — Exam- 
ination of  Fig.  i  shows  that  the  ventral  cavity  is  entirely 
closed,  though  some  of  the  organs  which  lie  in  it  are  hollow 
and  communicate  with  the  exterior.  On  the  head  we  find 
the  nose,  i,  and  the  mouth,  o,  opening  on  the  ventral  side, 
that  is,  on  that  surface  of  the  body  next  which  the  ventral 
cavity  lies.  The  nose  chamber  joins  the  mouth  chamber  at 
the  throat,  from  which  two  tubes  run  down  through  the  neck 
and  enter  the  ventral  cavity.  One  of  these  tubes,  placed  on 
the  ventral  side  of  the  other,  is  the  windpipe,  and  leads  to 
the  lungs,  /;  the  other  is  the  gullet,  and  leads  to  the  stomach, 
f»  From  the  stomach  another  tube,  the  intestine,  returns  to 
the  outside  at  the  lower  or  posterior  •(•  end  of  the  trunk. 
Mouth,  throat,  gullet,  stomach,  and  intestine  together  form 
the  alimentary  canal,  which  begins  in  the  head  above  or  an- 
terior to  the  ventral  cavity,  enters  this  cavity  at  the  bottom 
of  the  neck  and  runs  on  through  it,  to  pass  out  again  pos- 
teriorly ;  just  as  a  tube  might  pass  through  a  box,  in  at  one 
end  and  out  at  the  other,  without  opening  into  it  at  all.  In 

*  The  main  groups  in  which  animals  are  arranged  are  :  i.  Vertebrata, 
or  back-boned  animals.  2.  Mollusca,  including  snails,  slugs,  clams, 
oysters,  etc.  3.  Arthropoda,  including  flies,  moths,  beetles,  centipedes, 
lobsters,  spiders,  etc.  4.  Vermes,  including  worms  of  various  kinds.  5. 
Echinodermata  (hedgehog-skinned  animals),  including  sea-urchins,  star- 
fishes, etc.  6.  Ccelenterata,  the  sea  anemones  and  their  allies.  7.  The 
Protozoa,  all  microscopic  and  very  simple  in  structure. 

f  In  anatomy  the  head  end  of  an  animal  is  spoken  of  as  anterior,  and 
the  opposite  end  as  posterior,  no  matter  what  may  be  the  natural  stand- 
ing position  of  the  creature. 


TWO  CHIEF  CAVITIES   OF  THE  BODY.  7 

addition  to  the  lungs  and  the  greater  part  of  the  alimentary 
canal,  the  ventral  cavity  contains  several  other  organs,  among 
the  more  important  of  which  are  (Fig.  i)  the  heart,  h  ;  the 
kidneys,  k ;  the  sympathetic  nerve  centers,  s  •  and  the  large  di- 
gestive organs. 


FIG.  2. — A  diagrammatic  section  across  the  body  in  the  chest  region,  x,  the  dorsal 
tube,  which  contains  the  spinal  cord  ;  the  black  mass  surrounding  it  is  a  vertebra  ; 
rt,  the  gullet,  a  part  of  the  alimentary  canal;  A,  the  heart ;  sy.  sympathetic  nervous 
system;  //,  lungs;  the  dotted  lines  around  them  are  the  pleurae  ;  rr^  ribs  ;  st,  the 
breastbone. 

If  we  examine  a  section  made  across  the  trunk  of  the 
body,  say  about  the  level  of  the  middle  of  the  chest  (Fig.  2), 


FIG.  3. — A  sectioa  across  the  forearm  a  short  distance  below  the  elbow-joint.  R 
and  £7,  its  two  supporting  bones,  the  radius  and  ulna ;  <?,  the  epidermis  and  d,  the 
dermis,  of  the  skin  ;  the  latter  is  continuous  below  with  bands  of  connective  tissue,  j, 
which  penetrate  between  and  invest  the  muscles  (i,  2,  3,  4,  etc.)  ;  «,  n,  nerves  and 
vessels. 

we  find  on  the  dorsal  side  the  neural  tube,  x,  and  in  it  the 
spinal  cord,  which  is  not  represented  in  the  figure.  The 
part  surrounding  the  neural  tube  and  represented  by  the 


8  THE  HUMAN  BODY. 

black,  star-shaped  mass  is  part  of  the  spinal  column.  The 
chest  cavity  is  enclosed  by  the  spinal  column,  the  ribs  r,  r, 
and  the  breastbone  st,  and  contains  the  lungs,  /,  /;  the 
heart,  h  ;  the  gullet,  a ;  and  the  sympathetic  centres,  sy,  sy. 

The  Limbs. — If  our  section  is  made  across  one  of  the 
limbs,  we  find  no  such  arrangement  of  cavities.  Each  limb 
has  a  supporting  axis  made  of  one  or  more  bones  (as  seen  at 
U  and  R,  Fig.  3,  which  represents  a  section  made  across  the 
forearm  near  the  elbow  joint),  but  soft  parts,  chiefly  muscles, 
are  closely  packed  around  this  axis,  and  the  whole  is  en- 
veloped by  skin. 

Man's  Place  among  Vertebrates. — Although  man's  struc- 
tural plan  in  its  broad  features  simply  indicates  that  he  is  a 
vertebrate  animal,  yet  he  is  much  more  like  some  vertebrates 
than  others.  The  hair  covering  his  body,  and  the  organs 
producing  milk  for  the  nourishment  of  the  infant  by  its 
mother,  are  entirely  absent  in  fishes,  reptiles,  and  birds,  but 
are  possessed  by  ordinary  four-footed  creatures  and  by  whales, 
bats,  and  monkeys.  The  organs  which  form  milk  are  the 
mammary  glands,  and  all  kinds  of  animals  whose  females  pos- 
sess them  are  known  as  Mammalia  *  /  man  is,  therefore,  a 
Mammal.  One  of  the  most  important  characteristics  of  the 
Mammalia  is  a  cross-partition,  called  the  midriff 'or  diaphragm, 
(d,  Fig.  i )  which  separates  the  ventral  cavity  into  an  anterior 
and  a  posterior  part;  the  upper  or  anterior  story  is  the  chest 
or  thoracic  cavity;  the  lower  or  posterior,  the  abdominal  cavity. 
The  chest  contains  the  heart,  lungs,  and  most  of  the  gullet ; 

*  Zoologists  classify  vertebrate  animals  in  five  groups.  I.  Pisces,  in- 
cluding all  true  fishes,  as  sharks,  eels,  salmon,  shad,  perch,  etc.,  but  ex- 
cluding the  so-called  shellfish,  as  oysters,  clams,  and  lobsters,  which  are 
not  vertebrates  at  all.  2.  Amphibia,  frogs,  toads,  newts,  salamanders, 
etc.  3.  Reptilia,  lizards,  alligators,  turtles,  snakes.  4.  Aves,  birds.  5. 


MAN'S  PLACE  AMONG   VERTEBRATES.  9 

the  abdomen  contains  the  lower  end  of  the  gullet  (which 
pierces  the  diaphragm),  the  stomach,  the  intestine,  the  kid- 
neys, and  most  of  the  organs  making  digestive  liquids.  The 


22 


FIG.  4. — Diagram  showing  the  position  of  the  thoracic  and  abdominal  organs,     i 
lower  border  of  right  lung  ;  2,  the  same  of  the  left  lung  ;  3,  liver,  right  lobe  ;  4,  liver 
left  lobe  ;  5,  suspensory  ligament  of  the  liver  ;  6,  fundus  of  gall-bladder  ;  7,  cardia  o 
stomach  ;  8,  fundus  of  stomach  ;  g,  lower  border  of  stomach  ;  10,  position  of  pylorus 
n,  caecum;  12,  vermiform  appendix  ;  13,  ascending  colon  ;  14,  right  flexure  of  colon 
15,  transverse  colon  ;  16,  position  of  left  flexure  of  colon  ;  17,  descending  colon  ;  18 
portion  of  sigmoid  colon,  concealed  by,   19,  convolutions  of  the  small    intestine;  20, 
termination  of  ileum,  ascending  from  right  to  left ;  21,  bladder,  distended,  partly  cov- 
ered by  peritoneum  ;  22,  the  part  of  the  bladder  which  is  not  covered  by  peritoneum. 


10  THE  HUMAN  BODY. 

sympathetic  nerve  centres  run  through  both  abdomen  and 
chest,  and  extend  beyond  the  latter  into  the  neck. 

The  ventral  cavity,  opened  from  the  front,  but  with  its 
contents  undisturbed,  is  shown  in  Fig.  4.  We  there  see,  in  the 
chest,  the  lungs  and  the  heart,  the  latter  largely  covered  by 
the  lungs.  Below  the  diaphragm  is  the  abdominal  cavity, 
containing  the  liver,  the  stomach,  the  intestines,  and  the 
bladder. 

Summary. — Man  is  a  vertebrate  animal,  because  his  body 
presents  dorsal  and  ventral  cavities  separated  from  one  another 
by  a  hard  partition.  The  dorsal  cavity  contains  the  brain 
and  spinal  cord,  and  reaches  into  the  head.  The  ventral 
cavity  stops  at  the  bottom  of  the  neck  and  contains  the  main 
organs  of  circulation,  respiration,  and  digestion. 

Man  belongs  to  that  subdivision  of  vertebrates  known  as 
Mammalia  (i)  because  his  body  is  covered  by  hair;  (2)  be- 
cause of  the  presence  of  mammary  glands;  (3)  because  the 
ventral  cavity  is  completely  separated  by  the  diaphragm  into 
thorax  and  abdomen. 

That  man  is  intellectually  superior  to  any  other  animal,  and 
stands  supreme  in  the  world,  can  be  doubted  by  no  one, 
especially  when  we  consider  his  power  of  forming  concepts  of 
right  and  wrgng,  and  his  feeling  of  moral  responsibility.  But 
anatomists  have  only  to  deal  with  man's  body  as  a  material 
object,  and  as  such  they  classify  it  among  other  animal  bodies 
according  to  the  degree  of  resemblance  found  between  them. 


CHAPTER   II. 

THE  MICROSCOPICAL  AND   CHEMICAL  COMPOSITION  OF 
THE  BODY. 

What  are  the  Tissues  ? — Having  gained  some  idea  of  the 
general  arrangement  of  the  larger  parts  of  the  body,  we  may 
next  consider  the  minute  structure  of  the  tissues.  The  tissues 
are  made  up  of  cells*  which  are  so  small  that  a  single  one 
can  be  seen  only  with  the  help  of  a  microscope. 
In  a  fully  formed  cell  (Fig.  5)  we  find  three 
parts  :  (i)  a  cell  body  made  up  of  a  soft  gran- 
ular substance,  protoplasm  ;  (  2  )  a  smaller  and 
less  granular  cell  nucleus  embedded  in  the  cell 
body;  and  (3)  a  tiny  dot,  the  nucleolus,  lying 
in  the  nucleus.  Cells  vary  much  in  form  and 
size,  though  all  are  very  small.  A  great  many 
float  in  our  blood,  and  are  more  or  less  rounded 
(3).  Others  are  flattened  to  form  thin  scales 
as  in  Fig.  6,  which  represents  cells  scraped 
from  the  peritoneum,  the  membrane  lining  the  FIG.  s.— Forms 

,,/.,,,  of  cells  from   the 

wall  of  the  abdomen.      Still   otfrers  are   elon-    body. 
gated,  as  c,  Fig.  5.      If  greatly  elongated,  the  cell  becomes  a 
slender  thread,  called  a  fibre  ;  long  fibres  are  often  made  up  of 
these  elongated  cells,  joined  end  to  end.     Examples  of  fibres 
are  shown  in  Figs.  35  and  85.     Speaking  in  general,  we  may 

*  So  called  from  an  old  belief  that  they  were  little  bags  or  chambers. 
Most  cells  are  really  solid  or  semi-solid  throughout. 

II 


12  THE  HUMAN  BODY. 

say  that  the  whole  body  consists  of  tiny  cells,  either  rounded 
and  thick,  fiat  and  thin,  or  elongated  to 
form  fibres.  Just  as  a  wall  is  built  of 
distinct  bricks  or  stones,  so  an  organ  is 
made  up  of  a  number  of  cells. 

All   the   solid  parts  of  the  body  are 
either  cells  or  fibres  which  have  grown 
from  cells,  except  something  which  cor- 
responds   pretty    closely    to    the    mortar 
FIG.  6.— Fiat  ceils  from  which  lies  between  the  bricks  of  a  wall 

the  surface    of    the    lining 

membrane  of  the  abdomen  and    holds    them   together.      This   latter 

(peritoneum) :  #,  cell-body  ; 

&,  nucleus ;  c,  nucieoii.  material,  known  in  the  body  as  inter- 
cellular substance,  is  in  some  places  abundant,  in  others  scanty 
or  absent.  Wherever  found,  the  intercellular  substance  is 
made  by  the  cells  which  lie  embedded  in  it ;  they  pass  it  out 
from  their  surfaces  and  repair  it  when  necessary. 

Summary. — Cells  thus  essentially  make  up  the  body  and 
do  its  work;  their  form  and  arrangement  determine  the 
form  of  the  organs  ;  their  activity,  the  function  of  the  organs. 
For  example,  the  bone  cells  have  the  power  of  forming  the 
intercellular  substance  which  gives  the  hardness  to  the  bony 
skeleton  ;  the  muscle  cells  are  long  fibres  and  by  their  con- 
traction move  the  bones  to  which  they  are  attached  ;  the 
cells  embedded  in  the  wall  of  the  stomach  secrete  the  peculiar 
solvent  fluid  used  in  digestion. 

Anatomy  may  be  defined  as  the  study  of  the  forms  which  cells 
and  intercellular  substances  assume  ;  physiology,  as  the  study  of 
the  specific  activity  of  the  cells. 

The  Physiological  Division  of  Labor. — In  a  tribe  of 
wandering  savages,  living  by  the  chase,  we  find  that  each 
man  has  no  special  occupation  of  his  own  ;  he  collects  his 
own  food,  provides  his  own  shelter,  defends  himself  from 


MICROSCOPICAL   COMPOSITION  OF  THE  BODY.       13 

wild  beasts  and  his  fellow  men.  In  a  civilized  nation,  on 
the  contrary,  we  find  that  most  men  have  some  one  particu- 
lar business :  farmers  raise  crops  and  cattle ;  cooks  prepare 
food  ;  tailors  make  clothes  ;  and  policemen  and  soldiers  pro- 
tect the  property  and  lives  of  the  rest  of  the  community;  in 
other  words,  we  find  a  division  of  labor.  The  more  minute 
the  division  of  labor  in  a  nation,  the  more  advanced  is  it  in 
civilization  ;  so  also  an  animal  is  higher  or  lower  in  propor- 
tion as  the  duties  necessary  for  maintaining  its  existence  are 
distributed  among  different  tissues  and  organs.  The  amoeba, 
one  of  the  lowest  animals,  feels,  moves,  catches  and  digests 
food,  and  breathes,  although  it  consists  of  but  one  cell. 
Higher  animals  perform  these  functions  by  means  of  differ- 
ent cells  set  apart  in  special  organs.  This  specialization  of 
function  is  called  differentiation. 

Results  of  a  Division  of  Labor. — From  the  division  of 
employments  in  advanced  communities,  several  important 
consequences  result.  In  the  first  place,  when  every  one 
devotes  his  time  mainly  to  one  kind  of  work,  all  kinds  of 
work  are  better  done  :  the  man  who  always  makes  boots  be- 
comes more  expert  than  the  man  who  is  engaged  on  other 
things  also ;  he  can  not  only  make  more  boots  in  a  given 
time,  but  he  can  make  better  boots.  In  the  second  place, 
when  various  employments  are  distributed  among  different 
persons,  there  arises  a  necessity  for  a  new  kind  of  industry  in 
order  to  convey  the  special  product  of  any  individual  not 
needed  by  himself  to  others  who  may  want  it,  and  to  bring 
him  in  return  such  excess  production  of  others  as  he  may 
need.  The  conveyance  of  food  from  the  country  to  cities, 
and  of  manufactures  to  agricultural  districts,  are  examples  of 
this  sort  of  labor  in  civilized  communities.  Finally,  there  is 
developed  a  necessity  for  arrangements  by  which,  at  any 


*4  THE  HUMAN  BODY. 

given  time,  the  activity  of  individuals  shall  be  regulated  in 
accordance  with  the  wants  of  the  whole  community  or  of  the 
world  at  large. 

Exactly  similar  phenomena  result  from  the  division  of 
physiological  labor  in  the  human  body.  Each  tissue  and 
organ  does  a  special  work  for  the  whole  body  and  in  turn 
relies  on  the  others  for  their  aid  ;  thus  every  sort  of  neces- 
sary work  is  better  performed ;  the  tissue  or  organ,  since 
it  has  nothing  else  to  look  after,  is  constructed  with  reference 
only  to  its  own  particular  duty,  and  is  capable  of  doing  it 
extremely  well.  This,  however,  necessitates  a  distributing 
mechanism  by  which  all  excess  products  of  the  various  organs 
shall  be  carried  to  others  which  require  them;  and  a  regulat- 
ing mechanism  by  which  the  activities  of  each  shall  be  con- 
trolled in  accordance  with  the  needs  of  the  whole  body.  We 
accordingly  find  a  set  of  organs,  the  heart  and  blood  vessels, 
which  circulate  the  blood  so  that  in  its  course  through  the 
body  it  gets  something  from  and  gives  something  to  each 
organ  through  which  it  flows ;  and  a  set  of  nervous  organs 
which  ramify  in  every  direction  and  regulate  the  activity  of 
its  parts. 

The  Chemical  Composition  of  the  Body. — If  we  go  be- 
yond the  tissues  to  seek  the  ultimate  constituents  of  the  body, 
we  must  lay  aside  the  microscope,  and  call  upon  chemistry  to 
discover  what  elements  and  compounds  make  up  the  cells  and 
intercellular  substance. 

Elements  found  in  the  Body. — Of  the  many  elements 
discovered  by  chemists,  only  seventeen  have  been  found  in 
the  healthy  human  body.*  Very  few  exist  in  it  uncombined, 

*  The  elements  found  in  the  body  in  health  are  carbon,  hydrogen,  ni- 
trogen, oxygen,  sulphur,  phosphorus,  chlorine,  fluorine,  silicon,  sodium, 
potassium,  lithium,  calcium,  magnesium,  iron,  manganese,  and  iodine. 


CHEMICAL   COMPOSITION  OF  THE  BODY.  15 

although  some  oxygen  is  dissolved  in  the  blood  and  is  also 
found,  mixed  with  nitrogen,  in  the  lungs. 

Chemical  Compounds  existing  in  the  Body. — These  are 
so  numerous  that  it  would  be  a  long  task  to  enumerate  them, 
but  some  require  mention.  They  may  be  divided  into  organic 
and  inorganic.  The  general  distinguishing  characteristic  of 
the  organic  constituents  of  the  body  is  that  if  dried  they 
would  burn  in  a  fire  ;  of  the  inorganic  components,  that  they 
could  not  be  made  to  burn. 

Inorganic  Constituents  of  the  Body. — Of  the  inorganic 
constituents  of  the  body,  wafer  and  common  salt  are  the  most 
important ;  they  are  found  in  all  the  organs  and  liquids  of  the 
body.  Phosphate  and  carbonate  of  lime  are  also  found  in  large 
proportions  in  the  bones  and  teeth,  and  free  hydrochloric 
acid  (muriatic  acid)  is  always  found  in  healthy  gastric  juice, 
which  dissolves  some  kinds  of  food  in  the  stomach. 

Organic  Constituents  of  the  Body. — All  organic  con- 
stituents of  the  body  contain  carbon,  hydrogen,  and  oxygen  ; 
some  contain  nitrogen  also.  There  are  three  chief  kinds  of 
them,  viz. ,  albumens,  fats,  and  carbohydrates. 

Albuminous  or  Proteid  Substances. — These  are  by  far 
the  most  characteristic  organic  compounds  existing  in  the 
body ;  they  are  known  only  as  obtained  from  living  beings, 
as  they  have  never  yet  been  artificially  constructed  in  the 
laboratory ;  a  good  example  is  found  in  the  white  of  an  egg, 
which  consists  chiefly  of  albumen  dissolved  in  water.  All 
the  tissues  of  the  body  which  have  any  marked  physiological 
property  contain  some  albuminous  substance,  only  such  things 
as  hairs,  nails,  and  teeth  being  devoid  of  them.  All  albumin- 
ous bodies  contain  nitrogen,  carbon,  hydrogen,  and  oxygen  ; 
most  of  them  sulphur  and  phosphorus  in  addition.  The  more 
important  ones  found  in  the  body  are,  (i)  Serum  albumin, 


1 6  THE  HUMAN  BODY. 

which  is  very  like  egg  albumin,  and  is  found  dissolved  in  the 
blood;  (2)  Fibrin,  which  forms  in  blood  when  it  clots;  (3) 
Myosin,  which  is  found  in  the  muscles  and  which  by  "  setting  ' ' 
or  coagulating  after  death  causes  the  death  stiffening ;  (4) 
Casein,  which  is  found  in  milk,  and  forms  the  main  bulk  of 
cheese. 

Fats  belong  to  the  organic  compounds  in  the  body  which 
contain  no  nitrogen  ;  they  consist  solely  of  carbon,  hydrogen, 
and  oxygen.  The  chief  fats  in  the  body  are  palmitin,  stearin, 
and  olein  j  by  proper  chemical  treatment  each  can  be  split  up 
into  glycerine  and  a  fatty  acid,  i.e.  palmitic,  s/earic,  or  oleic 
as  the  case  may  be. 

The  Carbohydrates  also  consist  entirely  of  carbon,  hydro- 
gen, and  oxygen  ;  they  belong  to  the  same  class  of  substances 
as  starch  and  sugar.  The  most  important  carbohydrate  found 
in  the  body  is  glycogen,  a  sort  of  starch  found  stored  up  in 
the  liver  and  muscles.  Glucose  or  grape  sugar  also  exists  in 
the  body ;  and  lactose  or  milk  sugar  is  found  in  milk. 


PLATE    I.— THK  BONKS,   JOINTS,   AND  LIGAMENTS. 


EXPLANATION  OF  PLATE  I. 

A  front  view  of  an  adult  human  skeleton  to  illustrate  the  mode  in  which 
the  bones  are  connected  together  at  the  different  joints. 

For  the  names  of  the  bones  consult  the  description  of  Fig.   8,  which 
commences  on  page  20. 
a  Ligaments  of  the  Elbow  Joint. 
b  The  Ligament  which  is  connected  with  the  ventral  surfaces  of  the  bodies  of  the 

Vertebrae. 

e  Ligament  connecting  the  Innominate  Bone  to  the  Spine. 
f  Ligament  connecting  the  Innominate  Bone  to  the  Sacrum. 
g  The  Ligaments  of  the  Wrist  Joint. 
h  The  Membrane  which  fills  up  the  interval  between  the  two  bones  of  the  Fore 

Arm. 

/  A  similar  Membrane  between  the  two  bones  of  the  Leg,  and,  lower  down,  /,  liga- 
ments of  the  Ankle  Joint. 

k  A  Membrane  which  fills  up  a  hole  in  the  Innominate  Bone. 
»  Ligaments  of  the  Knee  Joint. 
oo  Ligaments  of  the  Toes  and  Fingers. 
p  Capsular  (bag-like)  Ligament  of  the  Hip  Joint. 
q  Capsular  Ligament  of  the  Shoulder  Joint. 


CHAPTER  III. 
THE    SKELETON. 

The  Skeleton  *  of  the  human  body  is  composed  of  three 
materials  :  bone,  cartilage,  and  connective  tissue. 

The  Bones  form  the  main  supporting  framework  of  the 
body,  and  determine  its  shape  ;  they  provide  levers  on  which 
the  muscles  pull,  and  they  surround  cavities  in  which  soft, 
delicate  organs,  as  brain,  spinal  cord,  and  heart,  may  lie  in 
safety. 

Cartilage  caps  the  ends  of  bones,  forming  elastic  pads 
with  smooth  surfaces  for  the  joints.  It  is  also  used  instead  of 
bone  in  some  parts  of  the  skeleton  where  considerable  flexi- 
bility is  required,  as  at  the  anterior  ends  of  the  ribs.  Carti- 
lage affords  one  of  the  best  tissues  of  the  body  for  the  exami- 
nation of  intercellular  substance.  A  thin  slice1  of  it  highly 
magnified,  Fig.  7,  shows  the  cartilage  cells,  #,  b,  scattered 
through  an  almost  structureless  material.  Very  young  cartilage 
consists  of  the  cells  only,  but  these  lay  down  intercellular  sub- 
stance around  them,  until  at  last  it  forms  the  main  bulk  of 

*  There  are  two  kinds  of  skeleton  in  the  animal  kingdom  :  the  external 
skeleton  or  exoskeleton,  and  the  internal  skeleton  or  endo skeleton.  The 
exoskeleton  is  made  by  the  skin,  either  in  it  or  on  it ;  examples  are  found  in 
the  shells  of  clams  and  lobsters;  the  scales  of  fishes  and  snakes;  the  tortoise- 
shell  of  turtles  ;  the  feathers  of  birds  ;  the  hair  and  claws  of  beasts.  In  man 
the  exoskeleton  is  only  slightly  developed  ;  hair,  nails,  and  teeth  belong  to 
it. 

17 


i8 


THE  HUMAN  BODY. 


the  cartilage,  and  gives  the  elasticity  and  flexibility  for  which 
cartilage  is  used  in  the  body. 


FIG  7.— A  thin  slice  of  cartilage  highly  magnified. 

Connective  Tissue  occurs  partly  in  the  form  of  stout  cords 
— ligaments — which  bind  different  bones  together,  or  which, 
as  tendons,  attach  muscles  to  bones.  It  partly  supplements 
the  coarser  bony  skeleton  by  a  fine  network  which  extends 
through  all  the  soft  parts  of  the  body  and  makes  a  sort  of 
microscopic  skeleton,  or  supporting  meshwork,  for  its  cells. 
It  is  laid  down  as  a  soft  packing  material,  a  good  deal  like 
raw  cotton,  in  the  crevices  between  different  organs,  as  shown 
at  s,  Fig.  8,  between  the  muscles  of  the  forearm.  This  tissue 
is,  in  fact,  so  widely  spread  through  the  body,  from  the  skin 


THE  SKELETON. 

outside  to  the  lining  of 
the  alimentary  canal  with- 
in, that  if  we  could  em- 
ploy a  solvent  which 
would  remove  everything 
except  this  connective 
tissue,  a  very  perfect 
model  of  all  the  organs 
would  be  left ;  something 
like  a  skeleton  leaf,  but  far 
more  minute  in  its  tracery. 
Articulations  and 
Joints. — If  the  pieces 
forming  the  hard  frame- 
work of  the  body  were 
put  together  like  the 
beams  and  planks  of  a 
frame  house,  the  whole 
mass  would  be  rigid  and 
immovable  ;  we  could  not 
raise  a  hand  to  the  mouth, 
or  put  one  foot  before  an- 
other. In  order  to  attain 
mobility  the  bony  skeleton 
is  made  up  of  more  than 
two  hundred  separate 
pieces,  joined  together ; 
the  points  where  they 
meet  are  called  articula- 
tions. An  articulation 
in  which  a  considerable 

range  Of  movement  is  per-     FIG.  8.— The  bony  and  cartilaginous  skeleton. 


20  THE  HUMAN  BODY. 

mitted  is  called  a  joint.  The  ends  of  bones  which  rub  against 
one  another  in  a  joint  are  covered  by  a  smooth  layer  of  carti- 
lage. 

The  Bony  Skeleton  (Fig.  8)  consists  of  an  axial  skeleton, 
supporting  head,  neck,  and  trunk,  and  an  appendicular  skele- 
ton, supporting  the  limbs  and  attaching  them  to  the  trunk. 

The  Axial  Skeleton. — The  fundamental  portion  of  this  is 
the  backbone,  spinal  column,  or  spine,  partly  seen  at  e  and  c, 
Fig.  8,  and  represented  isolated  from  the  rest  of  the  bones 
and  viewed  from  the  left  side  in  Fig.  9.  It  forms  an  axis,  on 
which  the  rest  of  the  body  is  carried.  On  the  upper  end  of 
the  vertebral  column  is  the  skull,  a,  b,  Fig.  8,  and  attached 
by  ligaments  to  the  under  surface  of  the  skull  is  the  hyoidbone, 
to  which  the  root  of  the  tongue  is  fastened. 

Slender  bones,  called  ribs,  are  attached  by  their  dorsal  ends 
to  the  sides  of  part  of  the  spine  ;  they  curve  round  the  sides  of 
the  chest  and  are  united  in  front  to  the  sternum,  or  breast-bone, 
d,  Fig.  8. 

Skull,  hyoid  bone,  vertebral  column,  ribs,  and  sternum  to- 
gether form  the  axial  skeleton. 

The  appendicular  skeleton  consists  of  the  pectoral  and  pelvic 
girdles,  attaching  the  limb  bones  to  the  axial  skeleton,  and 
of  the  limb  bones  themselves. 

The  Pectoral  Arch  or  Girdle  consists  on  each  side  of  a 
collar  bone  or  clavicle,  u,  and  a  shoulder  blade  or  scapula.  The 
scapula,  Pig.  8,  is  aflat,  triangular  bone,  lying  on  the  back  of 
the  chest  outside  the  ribs.  The  clavicle  is  a  slender  curved 
bone  like  an  italic  f  in  form.  Its  outer  end  is  attached  to 
the  scapula,  and  its  inner  end  to  the  top  of  the  sternum.  It 
serves  to  support  the  shoulder  joint,  and  to  prevent  it  from 
falling  backwards  or  inwards  toward  the  front  of  the  chest. 
It  is  absent  in  creatures  which  use  their  fore  limbs  for  walking 


PELWC  ARCH— SKELETON  OF  LOWER  LIMB. 


21 


only,  as  horses,  dogs,  and  cattle,  but   is  well  developed  in 
monkeys  and  bats. 

The  skeleton  of  the  upper  limb  consists  of:  (i)  The  arm 
bone  or  humerus,  t,  Fig.  8,  which  extends 
from  the  shoulder  to  the  elbow,  and  meets 
the  scapula  at  the  shoulder  joint ;  (2)  of 
two  forearm  bones,  the  radius,  g,  and  ulna, 
f,  the  radius  being  on  the  thumb  side ; 
and  (3)  of  twenty-seven  hand  bones.  Of  l 
the  hand  bones  eight,  the  carpal  bones,  h, 
lie  in  the  wrist  ;  five,  the  metacarpal  bones, 
i,  in  the  palm  of  the  hand ;  and  fourteen, 
\he  phalanges,  k,  in  the  thumb  and  fingers 
— two  for  the  thumb,  and  three  for  each 
finger. 

The  Pelvic  Arch  or  Girdle  consists  of 
a  single  bone,  the  os  innominatum,   s,   on 
each    side ;      this    is    firmly    fixed   at    its 
dorsal  end  to  the  lower  part  of  the  back- 
bone, meets  its  fellow  ventrally  at  the  lower 
end  of  the   abdomen,   and  bears   a   deep5 
socket  on    its  outer  side,   into  which  the, 
upper  end  of  the  thigh  bone  fits. 

The  Skeleton  of  the  Lower  Limb  con- 
sists of:    (i)  The  thigh  bone  or  femur,  r, 
the  longest  bone  in  the  body,  which  bears 
on  its  upper  end  a  hemispherical  knob  fit- 
ting into  a  hollow  on  the  outside  of  the 
os  innominatum,  to  form   the  hip  joint ; 
(2)  of  two  bones,  tibia  and  fibula,  /and  m,      the  spinal  column, 
in  the  lower  leg,  the  former  on  the  inside  ;    (3)  of  the  knee  cap 
or  patella,  y,  in  front  of  the  knee  joint  •    (4)  of  twenty-six  foot 


FIG.     . — Side  view  of 


22 


THE  HUMAN  BODY. 


bones.     Of  the  foot  bones  seven,  the  tarsal  bones,  n,  lie  below 
the  ankle  joint ;  five,  the  metatarsal  bones,  o,  are  anterior  to 


FIG.  10. — The  last  lumbar  vertebra  and  the  sacrum  seen  from  the  ventral  side. 


these  in  the  front  half  of  the  sole  of  the  foot ;  and  fourteen 
phalanges,  p,  are  found  in  the  toes,  two  in  the  great  toe  and 
three  in  each  of  the  others. 

The  Vertebral  Column  (Fig.  9). — The  upper  portion 
of  the  spine  consists  of  twenty-four  separate  bones,  each  called 
a  vertebra  ;  these  are  placed  one  above  the  other,  and  sepa- 
rated by  elastic  pads  of  cartilage  and  connective  tissue.  Seven 
vertebrae  {cervical,  C  1-7)  are  found  in  the  neck;  twelve 
(dorsal,  D  1-12)  lie  at  the  back  of  the  chest  and  carry  the 


A   VERTEBRA.  23 

ribs;  and  five  (lumbar,  L  1-5)  are  in  the  loins  or  "small  of 
the  back." 

Below  the  separate  vertebrae  we  find  the  sacrum  (Si), 
which  is  seen  in  Fig.  10,  with  the  lowest  lumbar  vertebra.  In 
childhood  the  sacrum  consists  of  five  distinct  vertebrae,  but 
these  grow  together  afterwards,  though  cross  ridges  remain  in- 
dicating the  original  lines  of  separation.  Below  the  sacrum, 
forming  the  tip  of  the  spine,  is  the  coccyx  (Co  1-4,  Fig. 9), 
a  single  bone  in  adults,  but  four  bones  in  children. 

The  Structure  of  a  Vertebra. — Those  vertebrae  which  re- 
main separate  resemble  one  another  in  general  form.  As  an 
example  we  may  take  the  eleventh  from  the  skull,  i.e.  the 
fourth  dorsal  vertebra  (Figs,  n  and  12). 


Ps 


FIG.  ii.  FIG.  12. 

FIG.  IT. — A  dorsal  vertebra  seen  from  behind,  i.e.  the  end  turned  from  the  head. 

FIG.  12. — Two  dorsal  vertebrae  viewed  from  the  left  side,  and  in  their  natural  rela- 
tive positions.  C,  the  body  ;  A ,  neural  arch  ;  Fv,  the  neural  ring  ;  Ps,  spinous  proc- 
ess ;  Pas,  anterior  articular  process;  Pa  i,  posterior  articular  process;  /Y,  transverse 
process  ;  Ft,  facet  for  articulation  with  the  tubercle  of  a  rib  ;  Fes,  Fci,  articular  sur- 
faces on  the  centrum  for  articulation  with  a  rib.  % 

In  it  we  find  (i)  a  thick  bony  mass,  C,  rounded  on  the 
sides  and  flattened  above  and  below  where  it  faces  its  neigh- 
bors, called  the  centrum  or  body  of  the  vertebra.  The  series 


24  THE  HUMAN  BODY. 

of  vertebral  bodies  forms  the  bony  partition  (<?,  e,  Fig.  i) 
already  mentioned  as  existing  in  the  trunk  between  the  neu- 
ral and  ventral  cavities.  (2)  The  arch,  A,  which  is  at- 
tached to  the  dorsal  side  of  the  centrum,  is  called  the  neural 
arch,  and  with  the  centrum  it  forms  the  neural  ring  {Fv).  By 
the  arrangement  of  the  vertebrae  one  above  the  other,  the 
successive  neural  rings  form  the  neural  tube,  in  the  cavity  of 
which  the  spinal  cord  lies.  (3)  Bony  processes  project  from 
the  body  and  the  arch  (Figs,  n  and  12)  :  these  are  (a)  the 
spinous  process  (Ps)  which  points  dorsally  and  with  its  fellows 
forms  the  ridge  of  the  spine  ;  (<$)  the  transverse  processes  (/V), 
one  on  either  side,  which  in  the  dorsal  region  support  the 
ribs;  and  (c~)  the  articular  processes  {Pas,  Pai),  four  on  each 
vertebra,  which  form  the  points  of  contact  with  the  adjoining 
vertebrae  above  and  below. 

Where  the  arch  joins  the  centrum  it  is  narrowed  to  a  stalk 
or  pedicle,  li,  Fig.  12.  When  the  vertebrae  are  placed  to- 
gether in  their  natural  relative  positions,  apertures  (Fi),  which 
lead  into  the  neural  canal,  are  left  between  their  narrower 
portions ;  through  these  apertures  (called  the  intervertebral 
foramina)  nerves  pass  into  or  out  from  the  spinal  cord. 

The  Atlas  and  Axis. — The  first  and  second  cervical  ver- 
tebrae, however,  differ  considerably  from  the  others.  The 
first,  called  the  atlas  (Fig.  13),  carries  the  head ;  it  has  a  very 
small  body  and  a  very  large  neural  ring.  A  ligan.ent,  Z, 
divides  the  ring  into  a  ventral  and  a  dorsal  portion ;  the 
spinal  cord  passes  through  the  latter  and  a  bony  peg,  D,  lies 
in  the  former.  The  peg  is  the  odontoid  or  tooth-like  process 
which  rises  from  the  second  cervical  or  axis  vertebra  (Fig.  14) 
and  forms  a  pivot  around  which  the  atlas,  carrying  the  skull 
with  it,  rotates  when  the  head  is  turned  from  side  to  side. 
On  the  anterior  (upper)  surface  of  the  atlas  are  a  pair  of  shal- 


SPINAL   COLUMN.  25 

low  hollows,  Fas.  A  pair' of  knobs  on  the  under  surface  of 
the  skull  (Fig.  20)  glide  in  these  hollows  during  nodding 
movements  of  the  head. 


Aa    Fas 


Pat 


FIG.  13.  FIG.  14. 

FIG.  13. — The  atlas.  FIG.  14. — The  axis.  Aa,  body  of  atlas.  Z>,  odontoid  proc- 
ess of  axis  ;  Fas,  facet  on  upper  side  of  atlas  with  which  the  skull  articulates  ;  and  in 
Fig.  13,  anterior  articular  surface  of  axis;  L,  transverse  ligament;  Frt,  vertebral  for- 
amen. 

Value  of  the  Structural  Arrangement  of  the  Spinal  Col- 
umn.— When  the  backbone  is  viewed  from  one  side  (Fig.  9) 
it  is  seen  to  present  four  curvatures  :  one  in  the  neck,  convex 
ventrally,  is  followed  by  a  curve  in  the  opposite  direction  in 
the  dorsal  region ;  in  the  loins  the  curvature  is  again  convex 
ventrally,  and  in  the  sacrum  and  coccyx  the  reverse  is  the  case. 
These  curves  add  greatly  to  the  springiness  of  the  spine,  and 
prevent  the  transmission  of  sudden  jars.  *  The  elastic  cushions 
(intervertebral  disks)  placed  between  the  bodies  of  the  verte- 
brae also  aid  in  protecting  the  delicate  brain  and  the  spinal 
cord  from  injury. 

The  intervertebral  disks  allow  of  a  certain  range  of  move- 
ment between  each  pair  of  vertebrae,  so  that  the  column  as  a 

*  Take  a  straight  but  tolerably  flexible  and  elastic  bar,  as  a  lath  or,  bet- 
ter still,  a  thin  steel  rod.  Hold  it  vertical,  with  one  end  resting  on  the 
floor,  and  give  a  smart  blow  on  the  upper  end  ;  the  jar  will  be  sudden 
and  violent.  Now  bend  the  rod  and  hit  it  again;  the  jar  will  be  much 
less,  as  the  curved  rod  yields  somewhat  to  the  blow  on  its  top. 


26  THE  HUMAN  BODY. 

whole  may  be  bent  in  any  direction.     On  the  other  hand, 
these  pads  and  the  ligaments  so  limit  the  movement  that  no 


FIG.  15. — The  ribs  of  the  left  side,  with  the  dorsal  and  two  lumbar  vertebrae,  the 
rib  cartilages,  and  the  sternum. 

sharp  bend  which  would  compress  or  injure  the  spinal  cord, 
can  occur  at  any  point. 


THE  SKULL. 


27 


The  sacral  vertebrae  are  separate  in  infancy,  but  grow  to- 
gether firmly  to  give  a  solid  support  to  the  pelvic  arch,  which 
transmits  the  weight  of  the  body  to  the  lower  limbs  when  we 

stand. 

Tsp 


Mel 


FIG.  16.— A  side  view  of  the  skull.  O,  occipital  bone;  T,  temporal;  TV,  parietal; 
&,  frontal;  S,  sphenoid;  Z,  malar;  MX,  maxilla;  N,  nasal;  £,  ethmoid;  L,  lach- 
"ymal;  Md,  inferior  maxilla. 

Summary. — The  backbone  is  rigid  enough  to  support  all 
the  rest  of  the  body ;  flexible  enough  to  bend  considerably  in 
any  desired  direction,  yet  not  sharply  at  any  one  point ;  and 


28  THE  HUMAN  BODY. 

elastic  enough  to  destroy  or  greatly  diminish  any  sudden  jar 
or  jerk  which  it  may  receive.  It  is  one  of  the  most  beautiful 
pieces  of  mechanism  in  the  body. 

The  Ribs  are  twenty-four  in  number,  twelve  on  each  side 
(Fig.  15).  They  are  slender  curved  bones  which  embrace 
the  sides  of  the  chest  and  are  attached  at  the  dorsal  end  to 
the  dorsal  vertebrae.  Ventrally  each  rib  ends  in  a  costal  car- 
tilage ;  the  cartilages  of  the  seven  upper  pairs  are  directly  ar- 
ticulated to  the  sides  of  the  breast-bone.  The  eighth,  ninth, 
and  tenth  rib  cartilages  join  the  cartilages  of  the  ribs  above ; 
the  eleventh  and  twelfth  are  not  attached  to  the  rest  of  the 
skeleton  at  their  ventral  ends  and  hence  are  known  as  the 
free  or  floating  ribs. 

The  Skull  (Fig.  16)  is  composed  of  twenty-eight  bones: 
eight  of  these  form  the  cranium  and  are  arranged  to  surround 
the  brain  and  protect  the  deep  parts  .  of  the  ears ;  six  lie 
inside  the  ears ;  and  the  remaining  fourteen  support  the  face, 
surround  the  mouth  and  nose,  and  (with  the  aid  of  some  of 
the  cranial  bones)  form  the  eye  sockets. 

The  Cranium  is  a  box  whose  thick  floor  (Fig.  i)  con- 
tinues anteriorly  the  partition  which  in  the  trunk  separates 
the  neural  from  the  ventral  cavity.  On  its  under  side  (Fig. 
20)  are  many  small  apertures  for  nerves  and  blood  vessels  to 
pass  in  or  out,  and  one  large  opening,  the  foramen  magnum, 
for  the  spinal  cord. 

The  cranial  bones  (Fig.  16)  are  the  following:  i.  The 
occipital  bone,  O,  which  lies  at  the  back  of  the  skull  and  has 
in  it  the  foramen  magnum.  2.  The  frontal  bone,  F,  which 
forms  the  forehead.  3.  The  parietal  bones ,  Pr,  two  in  num- 
ber, which  meet  one  another  above  the  middle  of  the  crown 
of  the  head,  and  form  a  large  part  of  the  roof  and  sides  of 
the  skull.  4.  The  temporal  bones,  T,  one  on  each  side, 


FACIAL  SKELETON— CRANIUM.  29 

which  contain  the  corresponding  ear  cavities.  5.  The  sphe- 
noid bone,  which,  with  the  occipital  bone,  forms  the  base  of  the 
skull,  and  sends  out  a  wing,  S,  on  each  side.  6.  The  ethmoid 
bone,  E,  which  forms  the  partition  between  the  brain  and 
nose  chambers,  and  part  of  that  between  the  nose  and  the 
eye  socket. 

The  Facial  Skeleton. — The  majority  of  the  face  bones 
are  in  pairs,  but  two  are  single;  one  of  these  is  the  lower 
jaw  bone  or  mandible,  Md,  Fig.  16  ;  the  other  is  the  vomer, 
which  forms  part  of  the  partition  between  the  two  nostrils. 

The  paired  face  bones  are:  i.  The  maxillce  or  upper  jaw 
bones,  MX,  which  carry  the  upper  teeth  and  form  most  of 
the  hard  palate  separating  the  mouth  from  the  nose.  2.  The 
palate  bones,  which  complete  the  bony  palate,  and  lie  in  front 
of  the  opening  (posterior  nares)  by  which  the  air  passes  from 
the  nasal  chambers  into  the  throat  cavity  (Fig.  20).  3.  The 
malar  or  cheek  bones,  Z.  4.  The  nasal  bones,  N,  roofing  in 
the  upper  part  of  the  nose.  5.  The  lachrymal  or  tear  bones, 
L,  small  and  thin,  between  the  eye  socket  and  the  nose.  6. 
The  inferior  turbinate  or  spongy  bones,  which  lie  inside  the 
nose,  one  on  the  outer  side  of  each  nostril  chamber. 

The  Cranial  Sutures. — All  the  bones  of  the  skull,  except 
the  lower  jaw  bone,  are  immovably  joined  together.  The 
edges  of  most  of  the  cranial  bones  interlock  in  a  manner 
similar  to  the  dovetail  joint  of  cabinet-makers.  Each  bone 
has  notched  edges  which  fit  accurately  into  hollows  of  the 
adjacent  bone;  this  kind  of  articulation  (or  suture)  is  well 
shown  in  Fig.  16. 

Comparison  of  the  Upper  and  Lower  Limbs  and  their 
Supporting  Arches. — The  bones  of  the  leg  and  arm  have 
already  been  enumerated,  but  certain  resemblances  and  differ- 
ences between  the  two  (Fig.  17)  are  worth  noting.  It  is 


THE  HUMAN  BODY. 


clear  that  they  correspond  very  closely  to  one  another  in 
general  structure;  the  pectoral  arch  answers  to  the  pelvic; 

Cd 


FIG.  17. — The  skeleton  of  the  arm  and  leg.  H,  the  humerus  ;  Cd,  its  articular 
head  which  fits  into  the  glenoid  fossa  of  the  scapula ;  £/,  the  ulna  ;  R,  the  radius  ;  O, 
the  olecranon  ;  Fe,  the  femur  ;  />,  the  patella ;  Ft,  the  fibula  ;  T,  the  tibia. 

the  humerus  to  the  femur ;  the  radius  and  ulna  to  the  tibia 
and  fibula;    five  metacarpal  bones  correspond  to  five  meta- 


SHOULDERS  AND  PELYIS.  31 

tarsal,  fourteen  phalanges  in  the  digits  of  the  hand  to  four- 
teen in  the  digits  of  the  foot ;  and  elbow  and  wrist  joints,  to 
knee  and  ankle.  There  is,  however,  in  the  arm  no  separate 


JL 

FIG.  18.— The  skeleton  of  the  trunk  and  the  limb  arches  seen  from  the  front.  C, 
clavicle ;  S,  scapula ;  (?<:,  innominate  bone  attached  to  the  side  of  the  sacrum  dor- 
sally  and  meeting  its  fellow  at  the  pubic  symphysis  in  the  ventral  median  line. 

bone  at  the  elbow  answering  to  the  patella  at  the  knee  ;  but  the 
ulna  bears  a  bony  process,  O,  which  is  in  early  life  a  separate 
bone  and  may  be  considered  as  corresponding  to  the  patella. 
There  are  in  the  adult  carpus  eight  bones,  in  the  tarsus  but 


3 2  THE  HUMAN  BODY. 

seven ;  here  again  we  find,  however,  that  originally  the 
astragalus,  Ta  (Fig.  19),  of  the  tarsus  consists  of  two  bones. 
The  elbow  joint  bends  ventrally  and  the  knee  joint  dorsally. 

When  we  compare  the  functions  of  the  limbs  greater  dif- 
ferences appear.  The  arms  have  their  parts  light  and  mova- 
ble to  serve  as  prehensile  organs ;  the  lower  limbs  have  their 
parts  heavy  and  firmly  knit  together  to  carry  the  weight  of 
the  body.  Accordingly  we  find  the  shoulder  girdle,  C,  S 
(Fig.  1 8),  attached  to  the  axial  skeleton  only  by  the  ventral 
ends  of  the  collar  bones,  and  hence  it  is  free  to  make  con- 
siderable movement,  as  in  "shrugging  the  shoulders."  The 
pelvic  girdle,  Oc,  on  the  contrary,  is  firmly  and  immovably 
attached  to  the  sides  of  the  sacrum. 

The  socket  on  the  outer  end  of  the  shoulder  blade,  which 
receives  the  upper  end  of  the  humerus  to  form  the  shoulder 
joint,  is  very  shallow,  and  allows  much  freer  movement  than 
the  deeper  socket  of  the  pelvis,  into  which  the  top  of  the 
femur  fits. 

If  we  hold  one  humerus  tightly  and  do  not  allow  it  to 
rotate,  we  can  still  move  the  forearm  bones  so  as  to  turn  the 
palm  of  the  hand  up  or  down ;  no  such  movement  is  possible 
between  tibia  and  fibula. 

In  the  foot  the  bones  are  much  less  movable  than  in  the 
hand,  but  are  so  arranged  as  to  make  an  elastic  arch  (Fig. 
19)  springing  from  the  rear  end  of  the  heel  bone,  Ca,  to  the 
anterior  ends,  Os,  of  the  metatarsal  bones.  When  we  stand, 
the  weight  of  the  body  rests  on  the  articular  surface  (Ta)  at 
the  crown  of  the  arch. 

The  toes  are  far  less  mobile  than  the  fingers,  the  difference 
between  great  toe  and  thumb  being  especially  marked. 
The  thumb  can  be  made  to  meet  each  of  the  finger  tips,  so 
that-  the  hand  can  seize  and  manipulate  very  small  objects, 


PECULIARITIES  OF  THE  HUMAN  SKELETON.         33 

wnereas  this  power  ot  opposing  the  great  toe  to  the  others  is 
nearly  absent  in  the  foot  of  civilized  man.  In  infants,  and  in 
savages  who  have  never  worn  boots,  the  great  toe  is  often 
movable,  though  it  never  acts  so  completely  like  a  thumb  as 

Ta 

en  Mr^     S{H 


Ti       Cl,     **SfH          T 

FIG.  19.—  The  bones  of  the  foot.  Co.,  Calcaneum,  or  heel  bone  ;  Ta,  articular 
surface  for  tibia  on  the  astragalus  ;  Cb,  the  cuboid  bone. 

it  does  in  most  apes,  which  use  their  feet  for  prehension  nearly 
as  much  as  their  hands.  Our  own  toes  by  practice  can  be 
made  more  movable  ;  persons  born  without  hands  have  learned 
to  write  and  paint  with  the  feet. 

Peculiarities  of  the  Human  Skeleton. — Our  power  of  main- 
taining an  erect  posture  and  of  walking  without  the  aid  of  the 
hands  gives  rise  to  interesting  peculiarities  in  the  structure  of 
the  human  skeleton.  In  no  other  vertebrate  is  the  division  of 
labor  between  the  anterior  and  posterior  limbs  carried  so  far; 
even  the  highest  apes  often  use  the  hand  in  locomotion  and  the 
foot  for  prehension.  As  characteristic  of  man's  skeleton  we 
may  note : 

i.  The  skull  is  nearly  balanced*  on  the  top  of  the  verte- 
bral column  (Fig.  20),  so  that  but  little  effort  is  needed  to  keep 
the  head  erect.  In  four-footed  beasts  the  skull  is  carried  on  the 

*  The  balance  is,  however,  not  quite  complete.  When  any  one  goes  to 
sleep  in  an  ill-ventilated  lecture-room  he  is  usually  awakened  by  a  sharp 
jerk  downwards  of  his  chin.  Since  the  muscles  concerned  in  holding  the 
head  erect  have  relaxed  their  vigilance,  the  greater  weight  of  the  front 
half  of  the  skull  exerts  its  effect. 


34 


THE  HUMAN  BODY. 


ci-,i'na1 
Spinal 


front  end  of  a  horizontal  backbone,  and  therefore  needs  spe- 
cial ligaments  and  considerable  mus- 
cular effort  to  support  it  ;  in  apes  the 
skull  does  not  balance  on  the  top  of 
the  spine,  because  the  face  is  much 
heavier  than  the  brain.  Therefore 
to  keep  the  head  erect  and  look 
things  straight  in  the  face  "  like  a 
man  '  '  is  very  fatiguing  and  the  po- 
sition cannot  long  be  maintained. 
In  men,  on  the  contrary,  the  face 
bones  are  relatively  smaller  and  the 
cranium  larger,  so  that  this  position 

FiG.  20.—  The  base  of  the  skull. 

The  lower  jaw  has  been  removed.    fs  maintained  with 
At  the  lower  part  of  the  figure  is 

the  hard  palate  forming  the  roof  -       TVi^      human 

of  the  mouth  and  surrounded  by  2'      i  ne      nUman 

the   upper  set  of  teeth.     Above        r,  •  j    r  J.T-       f 

this  are  the  paired  openings  of  When  VlCWCd  from  the  front,  IS  SCCll 
the  posterior  nares,  and  a  short  .  ,  i  -n  /• 

way  above  the  middle  of  the  fig-  to  widen  gradually  from  the  neck  to 

ure  is  the  large  median  foramen 

magnum,  with  the  bony  convex-  the  sacrum,  and  is,  therefore,  well  fit- 

ities     (or      occipital      cotidyles) 

which  articulate  with  the  atlas,  ted  to  sustain  the  weight  of  the  head, 

on  its  sides.     It  will  be  seen  that 

:  uPPer    limbs>   etc"       Its    Curvatures, 
/  which    are    peculiarly    human,     add 

the  occipital  condyles  would    be  .  .  j      ,       ,  •    .  , 

much  larger  than   that  behind  greatly  to  its  spring  and  elasticity. 

3.   The    pelvis,    to    the    sides    of 

which  the  lower  limbs  are  attached,  is  relatively  broad  in  man, 
so  that  the  balance  of  the  trunk  on  the  legs  is  more  strongly 
maintained. 

4.  The  lower  limbs  are  proportionately  much  longer  than 
the  arms  in  man.  This  makes  progression  on  them  more 
rapid  by  allowing  a  longer  stride,  and  also  makes  it  difficult 
to  go  on  <  '  all  fours  '  '  except  by  creeping  on  the  hands  and 
knees.  The  arms  of  some  apes  are  as  long  as,  and  of  others 
longer  than,  their  legs. 


PECULIARITIES  OF  THE  HUMAN  SKELETON.          35 

5.  The  arched  instep  and  broad  sole  of  the  human  foot  are 
very  characteristic.  Most  beasts,  as  horses,  walk  on  the  tips 
of  their  toes,  and  the  hoof  is  really  a  very  big  toe  nail; 
others,  as  bears,  place  the  heel  on  the  ground  to  be  sure,  but 
have  a  less  well-developed  tarsal  arch  than  man.  The  vaulted 
human  tarsus,  made  up  of  a  number  of  small  bones,  each  of 
which  can  glide  a  little  over  its  neighbors,  but  none  of  which 
can  move  much,  is  admirably  calculated  to  break  any  jar 
which  might  be  transmitted  to  the  spinal  column  by  the  inter- 
mittent contact  of  the  sole  with  the  ground.*  A  well -arched 
instep  is  therefore  rightly  considered  beautiful ;  it  makes  the 
gait  easier  and  more  graceful. 

*  A  carriage  spring  consists  of  two  curved  elastic  steel  bars  fastened  to- 
gether at  their  ends,  with  their  concave  sides  turned  towards  one  another. 
The  axle  of  the  wheel  is  attached  to  the  middle  of  the  lower  bar,  and  the 
weight  of  the  carriage  bears  on  the  middle  of  the  upper.  When  the 
wheel  jolts  over  a  stone  the  jerk  is  transmitted  to  the  elastic  arches,  which 
are  each  flattened  a  little,  so  that  instead  of  a  sudden  jerk  a  gentle  sway  is 
transmitted  to  the  carriage.  The  tarsal  arch  of  the  human  foot  acts  like 
the  upper  half  of  a  carriage  spring. 


CHAPTER   IV. 

THE   STRUCTURE,   COMPOSITION,    AND   HYGIENE  OF 
BONES. 

The  Gross  Structure  of  Bones. — Although  the  bones  differ 
very  much  in  shape,  all  are  alike  in  microscopic  structure  and 
in  chemical  composition.  When  alive  they  have  a  bluish- 
white  color,  with  a  pinkish  hue  if  blood  is  flowing  through 
them;  they  possess  considerable  flexibility  and  elasticity; 
this  may  be  best  observed  in  a  long  slender  bone,  as  a  rib.* 

To  get  a  general  idea  of  the  structure  of  a  bone  we  may 
select  the  humerus  (Fig.  21).  When  fresh  this  is  closely 
covered  by  a  tough  membrane,  the  periosteum,  composed  of 
connective  tissue  and  containing  many  blood  vessels.  During 
the  growth  of  the  bone  the  periosteum  deposits  new  bony 
tissue  upon  it  and  is  concerned  in  its  nourishment  through- 
out life.  When  it  is  stripped  off,  the  bone  dies.f  The 
periosteum  covers  the  humerus  except  on  its  ends  (Cp,  Tr, 
Cpl)  in  the  shoulder  and  elbow  joints,  where  the  bone  is 
covered  by  a  thin  layer  of  gristle  or  cartilage.  Very  early 
in  life  the  whole  humerus  consists  of  cartilage ;  this  is  after- 

*  The  rib  of  a  sheep  or  a  rabbit  when  thoroughly  boiled  can  be  readily 
scraped  clean  and  preserved,  and  serves  admirably  to  show  the  flexibility 
and  elasticity  of  bone. 

•{•  Cases  have  been  recorded  in  which  a  considerable  portion  of  a  bone 
or  even  the  whole  bone  has  been  removed  during  life,  and  the  periosteum 
(left  but  slightly  injured)  has  formed  a  new  bone  in  place  of  the  old. 

36 


STRUCTURE  OF  BONES. 


37 


Tmj 


Cpi 


Em 


FIG.   -zx.— The  right  humerus,  seen   from 
the  front.     For  description,  see  text. 


FIG.  22  —The  humerus 
cut  open.  a,  marrow 
cavity  ;  £,  hard  bone  ;  <:, 
spongy  bone;  d,  carti- 
lage. 


38  THE  HUMAN  BODY. 

wards  absorbed  and  replaced  by  bone,  leaving  only  a  thin 
layer  of  articular  cartilage  on  each  end. 

The  bone  itself  consists  of  an  almost  cylindrical  middle 
portion  or  shaft  (extending  between  the  dotted  lines  X  and 
Z)  and  two  articular  extremities.  These  extremities  are  en- 
larged to  give  a  wider  bearing  surface  in  the  joints,  and  also 
to  provide  space  on  which  to  attach  the  muscles  which  move 
the  bone ;  the  various  knobs  on  the  extremities  and  the 
rough  patches  on  the  shaft  mark  areas  where  muscles  were 
fixed. 

Internal  Structure. — If  the  humerus  is  divided  lengthwise, 
we  find  that  its  shaft  is  hollow ;  the  space  is  known  as  the 
medullary  cavity,  and  in  life  is  filled  with  soft  fatty  marrow. 
Fig.  22  represents  such  a  longitudinal  section.  We  see  that 
the  marrow  cavity  extends  nearly  to  the  articular  extremities ; 
and  that  in  these  the  bone  has  a  loose,  spongy  texture,  with 
the  exception  of  a  thin  dense  layer  on  the  surface.  In  the 
shaft  the  compact  outer  layer  is  thick,  whereas  the  spongy 
portion  forms  only  a  thin  stratum  next  the  medullary  cavity.* 
To  the  unassisted  eye  the  spongy  (cancellated)  bone  appears 
made  up  of  a  trellis-work  of  thin  bony  plates  which  intersect 
in  all  directions  and  surround  pin-head  cavities.  In  these 
spaces  there  is  found  during  life  a  substance  known  as  the  red 
marrow,^  which  is  quite  different  from  the  yellow  fatty  mar- 
row of  the  medullary  cavity. 

Why  Bones  are  Hollow. — If  the  bones  were  solid  and  of 
their  present  size,  they  would  be  extremely  heavy  J  and  un- 

*  These  facts  may  readily  be  demonstrated  by  sawing  in  two  length- 
wise the  bones  out  of  a  leg  of  mutton. 

f  The  red  marrow  forms  red  blood  corpuscles. 

\  Many  of  the  bones  of  birds  are  thin-walled  tubes  of  dense  bone  :  the 
central  cavity  contains  air  and  no  marrow,  and  communicates  by  tubes 
with  the  lungs.  Examine  the  humerus  of  a  pigeon  or  a  rooster. 


STRUCTURE  OF  BONES.  39 

necessarily  strong  for  the  common  purposes  of  life ;  if  they 
were  solid  and  of  their  present  weight,  they  would  not  give 
sufficient  surface  for  the  attachment  of  muscles,  and  would  be 
easily  broken.  It  is  a  well-known  principle  in  practical 
mechanics  that  a  tube  will  bear  a  greater  strain  than  a  solid 
rod  of  the  same  length  and  amount  of  material ;  hence  iron 
pillars  are  cast  hollow,  for  if  solid  they  would  be  enormously 
heavier  without  a  proportionate  increase  in  strength.  Take 
a  glass  tube  and  a  glass  rod  each  of  the  same  length  and 
weight ;  support  each  at  its  ends  and  hang  weights  on  the 
middle  until  it  breaks :  the  tube  will  be  found  to  bear  a 
much  greater  strain  before  breaking.  We  see  an  application 
of  this  same  principle  in  the  hollow  stalks  of  grass,  wheat, 
and  barley  and  in  the  frames  of  bicycles. 

Varieties  of  Structure  Found  in  Different  Bones. — Bones 
which,  like  the  humerus  and  femur,  present  a  shaft  and 
articular  extremities  are  called  long  bones ;  other  examples 
are  tibia  and  fibula,  radius  and  ulna,  metacarpal  and  meta- 
tarsal  bones,  and  the  phalanges  of  fingers  and  toes.  Tabular 
bones  form  thin  plates,  like  those  of  the  roof  of  the  skull, 
and  the  shoulder  blades.  Short  bones  are  rounded  or  angular, 
and  not  much  longer  in  one  diameter  than  another,  as  the 
carpal  and  tarsal  (Fig.  19)  bones.  Irregular  bones  include 
all  which  do  not  fit  well  into  any  of  the  above  classes ;  they 
usually  lie  in  the  middle  line  of  the  body  and  are  divisible 
into  similar  right  and  left  halves ;  the  vertebrae  are  good 
examples. 

All  bones  are  covered  by  periosteum  except  where  they  enter 
into  the  formation  of  a  joint,  but  in  the  human  body  only  the 
long  bones  possess  a  medullary  cavity  containing  yellow  mar- 
row. The  rest  are  filled  up  by  spongy  bone,  covered  by  a 
thin  layer  of  ivory  bone,  and  have  red  marrow  in  their  spaces. 


40  THE  HUMAN  BODY. 

The  Histology  of  Bone. — The  microscope  shows  that  com- 
pact bone  is  really  porous,  and  differs  from  spongy  bone  only 
in  the  fact  that  its  cavities  are  much  smaller,  and  the  hard 
bony  plates  between  them  thicker.  If  a  thin  transverse  sec- 
tion of  the  shaft  of  long  bone  (Fig.  23)  is  examined  with 
a  microscope  magnifying  about  twenty  diameters,  even  its 
densest  part  will  show  numerous  openings  which  become 
gradually  larger  near  the  medullary  cavity  and  pass  insensibly 
into  the  spaces  of  the  spongy  bone  around  it.  These  openings 


B 


FIG.  23. — A,  a  transverse  section  of  the  ulna,  natural  si/e,  showing  the  medullary 
cavity.     J3,  the  more  deeply  shaded  part  of  A  magnified  twenty  diameters. 

are  the  cross-sections  of  tubes  known  as  the  Haversian  canals, 
the  majority  of  which  run  through  the  bone  in  the  direction 
of  its  long  axis  and  are  united  by  numerous  cross  branches.  The 


HISTOLOGY  OF  BONE  41 

> 

outermost  Haversian  canals  open  on  the  surface  of  the  bone 
beneath  the  periosteum,  where  they  receive  blood  vessels 
which  pass  through  them  to  convey  materials  for  the  bone's 
growth  and  nourishment. 

Around  each  Haversian  canal  is  a  series  of  plates  or 
lamellce  which,  with  the  canal,  form  an  Haversian  system  ;  the 
entire  bone  is  made  up  of  a  large  number  of  such  systems, 
with  the  addition  of  some  lamellae  which  lie  in  the  corners 
between  them,  and  some  which  have  been  formed  by  the 
periosteum  on  its  outer  surface.  In  the  spongy  bone  the 
Haversian  canals  are  very  large,  and  contain  red  marrow  as 
well  as  blood  vessels,  with  only  a  few  lamellae  around  each. 


FIG.  24. — A  small  piece  of  bone,  ground  very  thin  and  highly  magnified. 

If  a  bit  of  bone  is  still  more  magnified  (Fig.  24)  we  find 
that  very  small  cavities  called  lacunae  lie  between  the  lamel- 
lae ;  from  each  lacuna  radiate  many  extremely  fine  tubes,  the 
canalicuti,  so  that  it  looks  like  a  small  animal  with  a  great 
many  legs.  The  innermost  canaliculi  open  into  the  Haver- 


42  THE  HUMAN  BODY. 

sian  canal  of  the  system  to  which  they  belong,  and  those  of 
various  lacunae  communicate  with  one  another,  so  that  a  set 
of  passages  is  provided  through  which  liquid  which  transudes 
from  the  blood  vessel  in  the  Haversian  canal  can  ooze  through 
the  bone. 

In  a  living  bone  a  nucleated  cell,  or  bone  corpuscle,  lies  in 
each  lacuna.  These  are  the  remnants  of  those  cells  which 
built  the  bone,  by  making  intercellular  substance ;  each 
one  builds  a  sort  of  skeleton  around  itself  which  adheres  to 
the  skeletons  of  the  others  to  form  the  whole  bone. 

Chemical  Composition  of  Bone. — Apart  from  the  bone  cor- 
puscles and  the  soft  contents  of  the  Haversian  canals  and  of 
the  spaces  of  the  cancellated  bone,  the  hard  bony  substance 
proper  is  composed  of  animal  and  mineral  matters  so  inti- 
mately combined  that  the  smallest  distinguishable  bit  of  bone 
contains  both.  The  mineral  matters  give  the  bone  its  hard- 
ness and  rigidity,  and  form  about  two  thirds  of  its  weight 
when  dried.  They  may  be  removed  by  soaking  the  bone  in 
diluted  hydrochloric  acid,*  and  the  animal  or  organic  part 
of  the  bone  is  then  left  as  a  tough,  flexible  mass,  which  retains 
perfectly  the  shape  of  the  original  bone. 

When  the  bone  is  boiled  in  water,  the  greater  part  of  the 
animal  portion  is  turned  into  gelatine  (or  glue)  and  is  dissolved 
in  the  water.  Most  of  the  gelatine  which  we  buy  in  the  shops 
is  obtained  by  boiling  fresh  bones  in  a  closed  vessel  under 
high  pressure  \  in  this  way,  the  water  becomes  much  hotter 
than  when  boiled  in  the  air,  and  dissolves  out  the  gelatine 

*  Add  a  couple  of  ounces  of  hydrochloric  acid  to  a  pint  of  water  and 
place  a  sheep's  rib  in  the  mixture  for  a  day  or  so,  after  having  previously 
scraped  the  bone  clean,  and  boiled  it  to  get  rid  of  the  fat.  It  will  be 
found  so  flexible  that  a  knot  may  be  tied  in  it ;  the  specimen  may  be 
preserved  in  strong  brine  or  dilute  alcohol  from  year  to  year  for  exhibition 
to  a  class. 


HYGIENE  OF  SKELETON.  43 

more  quickly.  When  a  shin  of  beef  is  used  to  make  soup  the 
bones  are  put  in  as  well  as  the  flesh,  and  the  whole  is  kept 
boiling  for  hours  to  extract  the  gelatine.  The  animal  matter 
of  bone  gives  it  toughness  and  elasticity. 

The  earthy  portion  may  be  obtained  free  from  the  animal 
by  calcining  a  bone  in  a  bright  fire.  The  residue  is  a  white 
and  very  brittle  mass,  which  retains  perfectly  the  shape  of 
the  original  bone.  It  is  readily  powdered  and  then  forms 
bone  ash,  which  consists  chiefly  of  the  phosphate  and  carbon- 
ate of  calcium ;  most  of  the  phosphorus  of  commerce  is  ob- 
tained from  it.  If  the  burning  be  imperfect  the  animal  matter 
is  charred  but  not  altogether  burnt  away,  and  a  black  mass, 
known  as  animal  charcoal  or  "  bone  black,"  is  left. 

Hygiene  of  the  Bony  Skeleton. — In  early  life  the  animal 
matter  of  the  bones  is  present  in  larger  proportion  than  later; 
hence  the  bones  of  children  are  tougher,  more  pliable,  and 
not  so  easily  broken.  The  bones  of  a  young  child  are  toler- 
ably flexible  and  are  capable  of  being  distorted  by  a  long 
continued  severe  strain.  For  this  reason  it  is  important  that 
a  child  be  made  to  sit  straight,  when  writing  or  drawing, 
to  avoid  the  risk  of  producing  a  lateral  curvature  of  the  spinal 
column ;  and  children  should  not  be  made  to  sit  up  during 
the  first  year  or  to  walk  too  early,  as  their  bones  are  not 
rigid  enough  to  bear  the  weight  of  the  body.  The  readi- 
ness with  which  bones  yield  to  prolonged  pressure  in  early 
life  is  well  illustrated  by  the  distorted  feet  of  Chinese  ladies, 
and  by  the  extraordinary  forms  (Fig.  25)  which  some  races 
produce  in  their  skulls  by  tying  boards  or  bandages  on 
the  heads  of  the  children.  A  distorted  foot,  even  in  the 
United  States,  is  no  uncommon  thing  in  these  days  of  tight 
boots  and  high  heels.  The  latter  are  especially  bad,  for, 
instead  of  allowing  the  arch  of  the  foot  to  support  squarely 


44  THE  HUMAN  BODY. 

the  weight  of  the  body,  they  tilt  the  arch  forward  and  throw 
the  weight  upon  the  toes,  which  are  thereby  squeezed  into 
the  front  of  the  boot.  This  not  only  crushes  the  toes  and 
leads  to  deformities,  corns,  and  bunions,  but  makes  the  gait 
stiff,  inelastic,  and  ungraceful. 


FIG.  25. — Skull  of  a  child  of  the  tribe  of  Chinook  Indians  (inhabiting  the  neighbor- 
hood of  the  Columbia  River),  distorted  by  tight  bandaging  so  as  to  assume  the  shape 
considered  elegant  and  fashionable  by  the  tribe. 

In  advanced  life  the  animal  matter  of  the  bones  is  present 
in  deficient  amount,  and  hence  they  are  brittle  and  easily 
broken. 

An  infant  grows  rapidly  and  hence  needs  food  containing 
phosphate  of  lime,  which  is  the  chief  mineral  constituent  of 
bone.  Of  all  common  articles  of  diet,  milk  contains  most 
phosphate  of  lime  :  this  is  one  great  reason  of  its  value  as  a 
food  for  children. 

Fracture. — A  break  in  a  bone  is  called  a  fracture  ;  when 
it  is  a  clean  break  the  fracture  is  simple;  when  the  bone  is 
more  or  less  broken  into  bits  on  each  side  of  the  break  the 
fracture  is  comminuted;  when  the  soft  parts  also  are  lacerated, 
so  that  there  is  an  opening  from  the  skin  to  the  broken  bone, 
the  fracture  is  compound. 

If  a  bone  is  broken  the  muscles  attached  to  it  tend  to  pull 
its  ends  out  of  place;  hence  it  requires  to  be  "set,"  and 


HYGIENE  OF  SKELETON.  45 

then  kept  in  position  by  splints  or  bandages ;  this  frequently 
needs  much  skill  and  a  thorough  knowledge  of  the  anatomy 
of  the  body.  A  surgeon  should  be  summoned  at  once,  as  the 
parts  around  the  break  commonly  swell  very  rapidly  and  make 
the  exact  nature  of  the  fracture  hard  to  detect,  and  the  re- 
placment  of  the  displaced  ends  dirhcult. 


CHAPTER  V. 
JOINTS. 

The  Movements  of  the  Body  are  brought  about  by  means 
of  the  soft  reddish  flesh  known  as  the  muscles,  which  are  fa- 
miliar to  all  in  the  lean  of  meat.*  Muscles  have  the  power 
of  contracting  with  considerable  force  ;  they  pull  their  ends 
toward  one  another  and  swell  out  in  the  middle  (Fig.  29) ;  in 
other  words,  they  become  shorter  and  thicker.  With  few 
exceptions,  each  muscle  is  attached  by  its  ends  to  two  bones  f 
and  overlaps  the  joint  between  them.  When  the  muscle 
shortens,  or  contracts,  it  produces  movement  at  the  joint. 
The  bones,  joints,  and  muscles  thus  form  the  chief  motor 
mechanism  of  the  body. 

Joints. — Articulations  which  permit  of  movement  by  the 
gliding  of  one  bone  on  another  are  called  joints;  all  are  con- 
structed on  the  same  general  plan,  though  the  range  and 

*  In  many  animals  muscles  kept  most  constantly  in  use  are  much  red- 
der than  others,  as,  for  example,  the  leg  muscles  of  a  chicken,  which  are 
redder  than  those  of  the  wings  and  breast,  and  as  the  coloring  matter  is 
turned  brown  by  heat,  they  form  the  "dark  meat"  after  cooking  ;  in 
birds  which  fly  a  great  deal  the  breast  muscles  (which  move  the  wings) 
are  also  dark.  The  heart,  which  is  a  muscle  always  at  work,  is  deep 
red,  even  in  fishes,  most  of  whose  muscles  are  pale. 

•f-  As  an  example  of  a  muscle  not  attached  to  the  skeleton,  we  may  take 
the  orbicularis  oris,  which  forms  a  ring  around  the  mouth  opening,  be- 
neath  the  skin  of  the  lips  ;  when  it  contracts  it  closes  the  mouth,  or  if  it 
contracts  more  forcibly  purses  out  the  lips.  The  orbicularis  palpebrarum 
forms  a  similar  ring  around  the  eye  opening,  and  when  it  contracts 
closes  the  eye. 

46 


HIP  JOINTS. 


47 


direction  of  movement  permitted  differ  in  different  joints. 
As  an  example  we  may  take  the  hip  joint,  a  section  of  which 
is  represented  in  Fig.  26. 


FIG.  26. —  Section  through  the  hip  joint. 

On  the  outer  side  of  the  os  innominatiim  (oi,  Fig.  26)  is  a 
deep  hollow,  the  acetabulum,  which  receives  the  upper  end  of 
the  femur.  The  acetabulum  is  lined  by  a  thin  layer  of  car- 
tilage (c)  with  an  extremely  smooth  surface,  and  its  cavity 
is  also  deepened  by  a  cartilaginous  rim  (r).  The  upper  end 
of  the  femur  (y)  consists  of  a  nearly  spherical  head,  borne  on 
a  neck ;  this  head  is  covered  by  cartilage,  and  rolls  smoothly 
in  the  acetabulum  like  a  ball  in  a  socket. 

Ligaments  bind  the  ends  of  the  bones  together  to  prevent 
their  displacement  ;  they  are  composed  of  connective  tissue, 
are  extremely  pliable  but  cannot  be  stretched,  and  are  very 
tough  and  strong.  One  is  the  capsular  ligament  (c.  /. ),  which 
encloses  the  joint  in  a  bag  ;  another  is  the  round  ligament 


48  THE  HUMAN  BODY. 

(/.  /.),  Fig.  26,  which  passes  from  the  rim  of  the  acetabulum 
along  a  groove  in  the  bone  to  the  centre  of  the  round  head  of 
the  femur. 

Covering  the  inside  of  the  capsular  ligament  and  continued 
back  to  the  edge  of  the  cartilage  of  the  head  of  the  femur  is 
the  very  thin  synovial  membrane  (j),  composed  of  a  layer  of 
flat  cells.  This  pours  into  the  joint  a  small  quantity  of  synovial 
liquid,  which  resembles  in  consistency  the  white  of  a  raw  egg, 
and  plays  the  part  of  oil  in  a  machine  by  lubricating  the  joint 
and  enabling  it  to  move  smoothly  and  with  little  friction. 

In  its  natural  state  the  synovial  membrane  lies  so  that  there 
is  practically  no  cavity  left  in  the  joint.  The  joint  surfaces  are 
held  in  close  contact,  not  by  the  ligaments  (which  are  much  too 
loose  and  serve  mainly  to  prevent  such  excessive  movement  as 
might  roll  the  femur  out  of  its  socket),  but  by  the  many  strong 
muscles  which  pass  between  pelvis  and  thigh  bone  and  hold 
both  firmly  together.  In  addition,  the  pressure  of  the  atmos- 
phere is  transmitted  by  the  skin  and  muscles  to  the  exterior  of 
the  air-tight  joint,  and  helps  to  keep  its  surfaces  together.  If 
all  the  muscles  are  cut  away  from  around  the  hip  joint  of  a  dead 
body,  it  is  found  that  the  head  of  the  femur  is  still  held  in  its 
place  by  the  pressure  of  the  air  so  firmly  that  the  weight  of  the 
limb  will  not  draw  it  out ;  but  if  the  air  is  let  into  the  joint  by 
cutting  into  the  cavity,  the  thigh  bone  falls  as  far  out  of  place 
as  the  ligaments  will  let  it. 

In  all  joints  we  find  the  same  essential  parts  :  bones,  articular 
cartilages,  synovial  membrane, synovial  liquid,  and  ligaments.* 

Ball  and  Socket  Joints. — Such  a  joint  as  that  at  the  hip 

*  The  structure  of  joints  can  be  readily  seen  in  those  of  a  fresh  calf's  or 
sheep's  foot.  The  synovial  membrane  is  so  thin  and  so  closely  adherent 
to  the  parts  it  lines  that  a  microscope  is  needed  for  its  demonstration;  but 
all  the  other  parts  are  readily  made  out. 


BALL  AND  SOCKET  JOINTS.  49 

is  called  a  ball  and  socket  joint,  and  allows  a  greater  variety  of 
movement  than  any  other.  The  thigh  can  ( i )  be  flexed,  that 
is,  bent  so  that  the  knee  approaches  the  chest,  and  (2)  ex- 
tended or  straightened  again  ;  it  can  (3)  be  abducted 'so  that  the 
knee  is  moved  away  from  the  middle  line  of  the  body,  and 
(4)  adducted  or  brought  back  again  ;  the  limb  can  also  (5)  be 
circumducted 9  i.e.,  with  knee  and  ankle  held  rigid,  the  whole 
leg  is  swung  round  to  describe  a  cone,  of  which  the  apex  is  at 
the  hip  joint  ;  and  finally  (6)  rotated,  i.e.,  the  whole  limb 
rolled  to  and  fro  on  its  long  axis.  All  ball  and  socket  joints 
allow  these  movements  to  a  greater  or  less  extent. 

Another  important  ball  and  socket  joint  is  at  the  shoulder 
between  the  upper  end  of  the  humerus  and  the  hollow  (glen- 
oid fossa]  near  the  upper  outer  corner  of  the  shoulder  blade. 
The  glenoid  fossa  being  much  shallower  than  the  acetabulum, 
the  range  of  movement  possible  at  the  shoulder  is  greater 
than  at  the  hip  joint. 

Hinge  Joints. — In  this  form  the  bony  cavities  and  pro- 
jections are  not  spherical,  but  are  grooved  and  ridged  so  that 
one  bone  can  glide  over  the  other  in  one  plane  only,  to  and 
fro,  like  a  door  on  its  hinges. 

The  knee  is  a  hinge  joint ;  it  can  only  be  bent  and 
straightened,  oryfom/and  extended.  Between  the  phalanges 
of  the  fingers  we  find  also  hinge  joints  ;  another  is  found  be- 
tween the  lower  jaw  and  the  cranium,  allowing  us  to  open 
and  close  the  mouth.  The  latter  is  not,  however,  a  perfect 
hinge  joint ;  it  permits  also  slight  lateral  movements,  and 
a  gliding  motion  by  which  the  lower  jaw  can  be  thrust  forward 
so  as  to  bring  the  lower  range  of  teeth  outside  the  upper.* 

*  The  object  of  these  minor  movements  is  to  allow  us  to  chew  our  food  ; 
in  carnivora,  as  cats,  which  bite  but  do  not  chew,  the  lower  jaw  forms  3 
perfect  hinge  joint  with  the  cranium. 


5° 


THE  HUMAN  BODY. 


ff 


Pivot  Joints.  —  In  this  form  one  bone  rotates  about  an- 
other. A  good  example  is  found  between  the  first  and  sec- 
ond cervical  vertebrae  (Figs.  13,  14).  The  odontoid  process 
of  the  axis  reaches  up  into  the  neural  arch  of  the  atlas,  and 
is  kept  in  place  there  by  the  transverse  ligament,  which  does 
not  let  it  press  against  the  spinal  cord.  It  forms  a  pivot 
around  which  the  atlas  rotates,  carrying  the  skull  with  it 
when  we  turn  the  head  to  right  or  left. 

A  more  complicated  kind  of  pivot  joint  is  found  in  the 

forearm.  Lay  the  forearm 
and  hand  flat  on  a  table,  palm 
uppermost  (supination)  :  the 
radius  and  ulna  are  parallel. 
Without  moving  the  shoulder 
joint  at  all  turn  the  hand  over 
so  that  its  back  is  upward  (pro- 
nation):  the  radius,  carrying 
the  hand,  crosses  over  the  ulna* 
(Fig.  27,  A). 

The  lower  end  of  the  hume- 
rus  (Fig.  21)  has  a  large  artic- 
ular surface  ;  on  the  inner  two 
thirds  of  this,  Tr,  the  ulna  fits, 
and  the  grooves  and  ridges  of 
the  bones  interlock  to  form  a 
hinge  joint,  allowing  us  only  to 
bend  or  straighten  the  elbow 

.     .  ,-p.i  j.  /-,  ,1 

joint.      The   radius    fits    on    the 
rounded   outer  third,  Cpl,  and  rotates  there  when  the  hand 


radius;  £7.  ulna. 


*  The  movements  and  positions  of  the  bones  throughout  the  forearm 
and  elbow  joint  may  be  observed  by  means  of  deep  pressure  with  the 
fingers  of  the  other  hand, 


A  SPRAIN.  51 

is  turned  over,  the  ulna  forming  a  fixed  axis  around  which  it 
moves. 

Gliding  Joints  as  a  rule  permit  of  but  little  movement. 
Examples  are  found  between  the  closely  packed  bones  of 
the  carpus  and  of  the  tarsus  (Fig.  19),  which  slide  a  little 
over  one  another  when  subjected  to  pressure. 

Dislocations. — When  a  bone  is  displaced  at  a  joint  or 
dislocated,  the  ligaments  are  more  or  less  torn  and  other  sur- 
rounding soft  parts  injured.  This  generally  leads  to  inflam- 
mation and  swelling,  which  make  it  difficult  to  find  out  in 
what  direction  the  bone  has  been  displaced,  and  also  greatly 
add  to  the  difficulty  of  replacing  it,  or,  in  surgical  language, 
of  reducing  the  dislocation.  The  muscles  attached  to  it  are, 
moreover,  apt  to  pull  the  dislocated  bone  more  and  more 
out  of  place.  In  most  cases  the  reduction  of  a  dislocation 
can  only  be  attempted  with  safety  by  one  who  knows  the 
forms  of  the  bones  and  possesses  sufficient  anatomical  knowl- 
edge to  recognize  the  direction  of  the  displacement.* 

A  Sprain  is  an  injury  to  a  joint,  accompanied  by  strain- 
ing, twisting,  or  tearing  of  the  ligaments,  without  dislocation 
of  the  bones.  A  sprained  joint  should  as  a  rule  get  imme- 
diate and  complete  rest,  continued  for  weeks  if  necessary ;  if 
there  be  much  swelling  or  continued  pain,  medical  advice 
should  be  obtained.  Perhaps  a  greater  number  of  permanent 
injuries  result  from  neglected  sprains  than  from  broken  bones. 

*  Dislocations  of  the  fingers  can  usually  be  reduced  by  strong  pulling, 
aided  by  a  little  pressure  on  the  parts  of  the  bones  nearest  the  joint.  The 
reduction  of  a  dislocation  of  the  thumb  is  much  more  difficult,  and  can 
rarely  be  accomplished  without  skilled  assistance. 


CHAPTER  VI. 

THE    MUSCLES. 

The  Muscles  of  the  human  body  are  more  than  five  hun- 
dred in  number ;  they  vary  much  in  size,  from  tiny  ones  at- 
tached to  the  bones  of  the  ear  to  that  on  the  front  of  the  thigh 
(29,  PI.  II),  which  passes  from  the  pelvis  to  the  tibia  and  is 
eighteen  inches  or  more  in  length.  Whatever  their  size, 
muscles  have  a  similar  structure  and  the  same  properties ; 
their  variety,  forms,  and  sizes  depend  on  the  work  they  have 
to  do.  In  addition  to  their  primary  function  of  moving  the 
body  the  muscles  give  it  roundness  and  shapeliness  ;  they  also 
help  to  enclose  cavities,  as  the  abdomen  and  the  mouth  ;  and 
they  hold  bones  together  at  joints. 

The  Parts  of  a  Muscle. — In  its  commonest  form  a  muscle- 
consists  of  a  soft  red  middle  part,  called  its  belly,  which  tapers 
towards  each  end,  where  it  passes  into  one  or  more  dense,  white, 
inelastic  cords  (tendons],  made  of  connective  tissue,  which  at- 
tach the  muscle  to  parts  of  the  skeleton.*  In  Fig.  28  are  shown 

*  The  parts  of  a  muscle  may  readily  be  seen  in  that  which  forms  the 
calf  of  a  frog's  leg.  Put  a  teaspoonful  of  ether  in  a  quart  of  water,  im- 
merse a  frog  in  it,  and  cover  the  vessel.  In  a  minute  the  animal  will  be 
quite  insensible  ;  its  head  can  then  be  cut  oft  and  its  spinal  cord  destroyed 
by  running  a  pin  along  it,  without  causing  the  animal  any  pain.  Now 
make  circular  cuts  through  the  skin  at  the  top  of  the  thighs  and  then  peel 
the  skin  off  like  a  pair  of  hose  :  it  will  come  quite  easily  except  about  the 
knee  joint,  where  it  may  be  necessary  to  divide  carefully  one  or  two  tough 
bands.  On  the  skinned  leg  many  muscles  will  be  observed,  and  the  long 
slender  tendons  which  run  to  the  toes.  The  calf  muscle  will  be  seen  to 
end  below  in  a  strong  tendon  near  the  heel.  If  this  be  divided  and  the 

52 


'THE  PARTS  OF  A  MUSCLE. 


some  of  the  muscles  of  the  arm.  It 
will  be  seen  that  some  (i,  2,  3)  pass 
from  arm  to  forearm  :  others  (7,  6,  5, 
4,  8,  9)  start  from  the  forearm  bones 
and  pass  to  the  bones  of  the  hand ; 
near  the  wrist  they  end  in  slender 
tendons,  which  are  bound  down  into 
place  by  a  stout  cross-band  of  con- 
nective tissue.  The  skin  has  been 
dissected  away  from  the  back  of  the 
middle  ringer  to  show  the  endings  of 
tendons  on  its  phalanges. 

The  belly  of  a  muscle  is  its  work- 
ing part ;  it  receives  nerves  which 
when  excited  cause  it  to  contract. 
In  so  doing  it  pulls  on  the  tendons, 
and  they  transmit  the  pull  to  the 
parts  to  which  they  are  attached. 

The  tendons  are  often  quite  long, 
as  for  example  that  of  the  common 
extensor  muscles  of  the  fingers  (5, 
Fig.  28),  whose  belly  is  in  the  upper 
half  of  the  forearm,  but  whose  tendon, 
dividing  above  the  wrist,  is  dis- 
tributed to  the  joints  of  the  fingers. 
The  muscles  which  straighten  the 
thumb  (8,  9,  and  10)  are  also  seen  to 
have  long  slender  tendons.  This  ar- 
FIG.  28.— The  muscles  on  the  rangcment  makes  the  limbs  light  and 

back  of  the  hand,  forearm,  and 

lower  half  of  the  arm,  as  exposed    cl^nrl/^r 

on  dissecting  away  the  skin. 

muscle  turned  upwards,  it  will  be  found  to  have  at  the  upper  end  of  its 
thick  rounded  belly  a  pair  of  short  tendons. 


54  THE  HUMAN  BODY. 

Some  muscles  pass  over  two  joints  and  can  produce  move- 
ment at  either ;   the  biceps  of  the  arm.    fixed  above  to  the 


FIG.  29. — Back  view  of  the  muscles  of  the  trunk. 
FIG.  30.— Front  view  of  the  muscles  of  the  trunk. 

scapula  and  below  to  the  radius,  can  produce  movement  at 
either  the  elbow  or  the  shoulder  joint. 

The  shortening  of  a  muscle  when  it  contracts  is  shown  by 
the  movement  which  it  causes ;  the  thickening  and  hardening 
may  be  seen  and  felt  on  the  biceps  in  front  of  the  humerus 
when  the  elbow  is  bent,  or  in  the  ball  of  the  thumb  when  it 
is  moved  so  as  to  touch  the  little  finger.  The  swelling  and 
hardening  of  a  contracted  muscle  are  daily  illustrated  when 
one  schoolboy  invites  another  to  feel  his  *  'biceps." 


VARIETIES  OF  MUSCLES.  55 

The  Origin  and  Insertion  of  Muscles. — That  part  of  the 
skeleton  to  which  the  inner  (i.e.,  nearer  the  centre  of  the 
body)  end  of  the  muscle  is  attached  is  called  its  origin ;  that 
to  which  the  outer  is  attached  is  called  its  insertion.  Ordi- 
narily, the  origin  is  the  less  movable  end.  This  may  be  seen 
in  the  arm,  where  we  find  that  when  the  belly  of  the  muscle 


FIG.  31. — The  biceps  muscle  and  the  arm  bones,  to  illustrate  how,  under  ordinary 
circumstances,  the  elbow  joint  is  flexed  when  the  muscle  contracts. 

contracts  and  pulls  oh  its  tendons,  the  result  is  commonly  that 
only  the  forearm  (insertion)  is  moved,  the  elbow  joint  being 
bent  as  shown  in  Fig.  31  ;  the  shoulder  (origin)  is  firm  and 
serves  as  a  fixed  point.  The  distinction  is,  however,  only  rel- 
ative :  if  the  radius  were  held  immovable  the  muscle  would 
move  the  shoulder  toward  the  radius,  instead  of  the  radius 
toward  the  shoulder;  as,  for  example,  in  going  up  a  rope 
"  hand  over  hand." 

Varieties  of  Muscles. — Many  muscles  have  the  simple 
typical  form  of  a  belly  tapering  toward  each  end,  as  A, 
Fig.  32  ;  others  divide  at  one  end,  and  are  called  two-headed 
or  biceps  muscles,  and  some  are  even  three-headed  or  triceps 
(back  of  upper  arm).  On  the  other  hand,  some  muscles  have 
no  tendon  at  one  end,  the  belly  itself  being  attached  to  the 


5  6  THE  HUMAN  BODY. 

bone;  a  few  have  no  tendon  at  either  end.     Sometimes  a 
tendon  runs  along  the  side  of  a  muscle,  and  the  fibres  of  the 
ABC       latter  are  attached  to  it  obliquely  (B,  Fig. 
32);    such  a  muscle  is  called  penniform  or 
featherlike,   from   a  fancied  resemblance  to 
the  vane  of  a  feather  ;  or  a  tendon  may  run 
down  the  middle  of  the  muscle  (C),  which 
is    then  called  Mpenniform.      Sometimes  a 
tendon   is   found  in  the  middle  of  the  belly 
as  well  as  at  each  end  (Fig.  33);    such  a 
FIG.  32.  —  Diagrams  muscle    is    called   two-bellied    or    digastric. 

illustrating,  A,  typical 


al°ng    the    frOnt    °f   *€    abdomen, 

fo?£°  mliscfe  ;  C.Tbt  fr°m  the    Pdvis    tO    the    chest>    °n    each   side 
penniform  muscle.  Qf    ^    middle    line>    ig    &    1()ng    musde>     fa 

straight  muscle  of  the  abdomen  (rectus  abdominis);  it  \spoly- 
gastric,  consisting  of  four  bellies  separated  by  short  tendons. 
Many  muscles  are  not  rounded,  but  form 
wide,  flat  masses,  as  those  which  lie  beneath 
the  skin  on  the  sides  of  the  abdomen. 

How  the  Muscles  are  Controlled.  —  Most 
of  the  muscles  of  the  body  are  paired,  that  is,  FlG  33.A 
they  have  corresponding  muscles  upon  the  tn 
opposite  side.*  The  muscles  are  attached  to  the  bones 
in  such  a  way  as  to  cause  motion  in  all  directions  permitted 
by  the  joint.  Thus  some  muscles  oppose  others,  as,  for 
example,  the  biceps  muscle  (Fig.  31),  which  lies  in  front 
of  the  humerus  and  bends  the  elbow  joint,  antagonizes  the 
triceps  muscle,  -which  lies  behind  the  arm  bone  and  extends  the 
elbow  ;  when  the  biceps  contracts  the  triceps  relaxes,  and  vice 
versa.  This  orderly  working  is  carried  out  by  means  of  the 

*  The  single  muscles  cross  the  middle  line  and  are  made  up  of  similar 
right  and  left  halves;  examples  are  orbicularis  oris  and  the  diaphragm. 


THE  GROSS  STRUCTURE  OF  A  MUSCLE.  57 

brain  and  spinal  cord,  which,  through  the  nerves,  govern  the 
muscles  and  regulate  their  activity.  In  convulsions  these  con- 
trolling organs  are  put  of  gear,  and  the  muscles  are  excited  to 


FIG.  34. — Side  view  of  the  muscles  of  the  face  and  neck. 

contract  in  all  sorts  of  irregular  and  useless  ways  ;  antagonists 
pulling  against  one  another  at  the  same  moment  cause  the 
whole  body  to  become  rigid. 

The  Gross  Structure  of  a  Muscle. — Each  muscle  is  an 
organ  composed  of  several  tissues.  Its  essential  constituent  is 
numbers  of  striped  fibres  constituting  striped  muscular  tissue. 
These  are  supported  and  protected  by  connective  tissue,  in- 
tertwined with  blood  and  lymph  vessels  which  convey  nour- 


58  THE  HUMAN  BODY. 

ishment  and  carry  off  waste  matters,  and  penetrated  by 
nerves  which  govern  their  activity. 

A   loose  sheath   of  connective  tissue,  the  perimysium,  en- 
velops the  whole  muscle  in  a  sort  of  case  ;   from  it  partitions 

run  in  and  subdivide  the 
belly  of  the  muscle  into 
bundles  or  fasciculi  which 
run  from  tendon  to  ten- 
don, or  the  whole  length 
of  the  muscle  when  it  has 
no  tendons.  The  coarse- 

FIG.  35. — A  small  bit  of  muscle  composed  of  ,,  _ 

five  primary  fasciculi.     A,  natural  size  ;   £,  the  nCSS    Or    fineness     Ot     meat 
same  magnified,  showing  the  secondary  fasciculi 
of  which  the  primary  are  composed.  depends      On     the     size      of 

these  fasciculi,  which  may  be  readily  seen  in  a  piece  of  boiled 
beef.  In  good  carving,  meat  is  cut  across  the  fasciculi,  or 
"  across  the  grain,"  as  it  is  then  more  easily  broken  up  by  the 
teeth  ;  the  polygonal  areas  seen  on  the  surface  of  a  slice  of  beef 
are  cross  sections  of  the  fasciculi.  The  larger  fasciculi  are 
subdivided  by  fine  partitions  of  connective  tissue  into  smaller 
(Fig.  35),  each  consisting  of  a  few  muscular  fibres  enveloped 
in  a  close  network  of  minute  blood  vessels.  Where  a  muscle 
tapers  the  muscle  fibres  in  the  fasciculi  are  less  numerous,  and 
when  a  tendon  is  formed  they  disappear  altogether,  leaving 
only  the  connective  tissue. 

Histology  of  Muscle. — The  striped  muscular  tissue,  which 
gives  the  muscle  its  power  of  contracting,  is  found  when  ex- 
amined by  the  microscope  to  be  made  up  of  extremely  slender 
muscle  fibres,  each  about  one  inch  in  length,  but  most  of  them 
less  than  -^^  of  an  inch  across. 

Each  muscle  fibre  has  externally  a  thin  sheath  or  envelope, 
the  sarcolemma,  which  envelops  the  contracting  part  of  the 


PLAIN  MUSCULAR   TISSUE. 


59 


fibre.       This   latter  is  soft  and  almost  semi-fluid  ;    under  a 

microscope  it  is  seen  to  present  a  striped  appearance,  as  if 

made  up  of  alternating  dimmer  and   brighter 

transverse    bands    (Fig.     36).       After  death 

the  contents  of  the  fibre  solidify  and  death- 

stiffening  results  ;    at  the  same  time  the  fibre 

often  splits  up  into  a   number   of  very  fine 

threads    or  fibrillce,  which   were  formerly  re- 

garded as  true  constituents  of  the  living  mus- 

cular fibre. 

The  contraction  of  a  voluntary  muscle,  as 
the  calf  muscle  of  the  leg  of  a  frog,  is  very 
rapid,  as  the  entire  twitch,  including  contrac- 
tion and  relaxation,  takes  but  one  tenth  of  a 

Second. 

Plain    Muscular    Tissue,  —  The    muscles  bre  highly   magn- 

fied.   At  a  the  fibre 
hitherto  spoken  of  are  all  more  or  less  under  has    been    crushed 

ana  twisted  so  as  to 

the  control  of  the  will  ;   we   can  make  them  te*r.    its,    contents, 

while     the    tougher 


FIG.  36.—  A  small 
pece  of  muscular  fi- 


contract  or  prevent  this  as  we  choose; 

are  therefore  often  called  the  voluntary  mus- 

i        »       i  , 

cles.*      Ihere  are  in  the  body  other  muscles 


mains     untorn     and 

conspicuous. 


*  No  sharp  line  can  be  drawn  between  voluntary  and  involuntary  mus- 
cles; the  muscles  of  respiration  are  to  a  certain  extent  under  the  control  of 
the  will;  any  one  can  draw  a  long  breath  when  he  chooses.  But  in  ordi- 
nary quiet  breathing  we  are  quite  unconscious  of  their  working,  and  even 
when  we  pay  heed  to  it  our  control  of  them  is  limited;  no  one  can  hold 
his  breath  long  enough  to  suffocate  himself.  Indeed,  any  one  of  the 
striped  muscles  may  be  thrown  into  activity,  independently  or  even  against 
the  will,  as  we  see  in  the  *'  fidgets"  of  nervousness,  and  the  irrepressible 
trembling  of  extreme  terror.  Functionally,  when  we  call  any  muscle 
voluntary,  we  mean  that  it  may  be  controlled  by  the  will,  but  not  that  it 
necessarily  always  is  so.  Structurally,  the  heart  occupies  an  intermedi 
ate  place  ;  its  striped  fibres  resemble  much  more  those  of  voluntary  than 
of  involuntary  muscles,  but  its  beat  is  not  subject  to  the  will. 


60  THE  HUMAN  BODY. 

whose  contractions  we  cannot  control,  and  which  are 
hence  called  involuntary  muscles;  they  are  not  attached 
to  the  skeleton  directly,  nor  concerned  in  our  ordinary 
movements,  but  lie  in  the  walls  of  various  hollow  organs 


FIG.  37. — The  muscular  coat  of  the  stomach. 

of  the  body,  as  the  stomach  (Fig.  37),  the  intestines,  and  the 
arteries  ;  by  their  contractions  they  move  the  contents  of 
those  cavities.  Like  the  voluntary  muscles,  the  involun- 
tary consist  of  contractile  elements,  with  accessory  connective 
tissue,  blood  vessels,  and  nerves ;  but  they  are  much  shorter 
and  smaller,  and  their  fibres  have  a  very  different  appearance 
under  the  microscope.*  They  are  not  cross  striped,  but  are 
elongated  cells  united  by  a  small  amount  of  cementing 
material.  Each  cell  (Fig.  38)  is  flattened  and  tapers  off 
towards  its  ends  ;  in  its  centre  is  a  nucleus  with  one  or  two 

*  The  smooth  muscle  fibres  vary  much  in  size  in  different  organs. 
An  average  might  be:  Length  -^^  in.  to  ^  in.;  breadth  ^^  in.  to 
^1^  in.  They  are  thus  seen  to  be  about  as  long  as  the  voluntary  muscle 
fibres  are  broad. 


BEEF  TEA. 


61 


nucieoii,     The  cells  have  the  power  of  shortening  in  the  direc- 
tion of  their   long  axes,  but  are  very  slow  in 
their  action. 

Heart  Muscle.  —  The  muscular  tissue  of  the 
heart  is  not  under  the  control  of  the  will  ;  it, 
however,  is  cross  striped,  and  more  like  the 
voluntary  than  the  ordinary  involuntary  mus- 
cle, though  it  differs  from  both.  The  con- 
traction of  the  heart  muscle  is  slower  than 
that  of  voluntary  muscles,  but  more  rapid  than 
that  of  the  involuntary  muscles. 

Speaking  generally,  we  may  say  that  the 
movements  necessary  for  the  nutrition  of  the 
body  are  not  left  for  us  to  look  after,  but 
are  carried  on  by  muscles  which  work  invol- 
untarily; the  blood  is  pumped  by  the  heart, 
and  food  churned  in  the  stomach  and  passed 
along  by  the  intestines,  whether  we  think  ma«nified-> 
about  it  or  not. 

The  Chemical  Composition  of  Muscle.  —  Muscle  contains 
about  75  per  cent,  of  water  and  a  considerable  quantity  of 
salts.  Living,  resting  muscle  is  alkaline  ;  hard  worked  or 
dying  muscle  is  acid.  Its  chief  organic  constituents  are 
proteid  or  albuminous  substances  (p.  15),  and  of  these  the 
most  abundant  in  a  perfectly  fresh  muscle  is  myosin.  Soon 
after  death  the  myosin  clots.  Dilute  acids  dissolve  myosin 
and  turn  it  into  syntonin,  which  used  to  be  thought  the  chief 
proteid  of  muscle. 

Beef  Tea.  —  When  .can  meat  is  heated  its  myosin  is 
converted  into  a  solid  insoluble  substance  much  like  the 
white  of  a  hard  boiled  egg.  Hence  when  a  muscle  is  boiled 
most  of  its  proteid  is  coagulated  and  stays  in  the  meat  in- 


62 


THE  HUMAN  BODY. 


stead  of  passing  out  into  the  water.      Even  if  beef  be  soaked 
first  in  cold  water  this  is  still  the  case,  as  myosin  is  not  sol- 


FIG.  39. — Fibres  from  the  heart  showing  the  striations  and  the  junctions  of  the 
cells.  Highly  magnified. 

uble  in  water.*  It  follows  that  beef  tea  as  ordinarily  made 
contains  little  but  the  flavoring  matters  and  salts  of  the  beef, 
and  some  gelatin  dissolved  out  from  the  connective  tissue  of 
the  muscle.  The  flavoring  matters  make  it  taste  as  if  it  were 
a  strong  solution  of  the  whole  meat,  whereas  it  contains  but 
a  small  proportion  of  the  really  nutritious  parts,  which  are 
left  behind  in  tasteless  shrunken  shreds  when  the  liquor  is 
poured  off.  Some  things  dissolved  out  of  the  meat  make 
beef  tea  a  stimulant  to  the  nervous  system  and  the  heart,  but 
its  nutritive  value  is  small,  and  it  cannot  be  relied  upon  to 
keep  up  a  sick  person's  strength  for  any  length  of  time. 

*  To  get  over  this  difficulty,  various  methods  of  making  beef  tea  have 
been  suggested,  in  which  the  chopped  meat  is  soaked  an  hour  or  two  in 
strong  brine  or  in  very  dilute  muriatic  acid.  In  these  ways  the  myosin 
can  be  dissolved  out  of  the  beef;  but  the  product  has  such  ah  unpleasant 
taste  that  no  one  is  likely  to  swallow  it,  and  least  of  all  a  sick  person, 


EXPLANATION  OF  PLATE  II. 

A  view  of  the  muscles  situated  on  the  front  surface  of  the  body  seen  in 
their  natural  position.  It  must  be  understood  that  beneath  these  muscles 
many  others  are  situated,  which  cannot  be  represented  in  the  figure. 

Muscles  of  the  Face,  Head,  and  Neck  : 

1.  Muscle  of  the  Forehead.     This,  together  with  a  muscle  at  the  back  of  the  head, 
has  the  power  of  moving  the  scalp. 

2.  Muscle  that  closes  the  Eyelids.     The  muscle  that  raises  the  upper  eyelid  so  as  to 

open  the  eye  is  situated  within  the  orbit,  and  consequently  cannot  be  seen  in 
in  this  figure. 

3.  4,  5.  Muscles  that  raise  the  Upper  Lip  and  angle  of  the  Mouth. 

6,  7.  Muscles  that  depress  the  Lower  Lip  and  angle  of  the  Mouth.  By  the  action 
of  the  muscles  which  raise  the  upper  lip,  ana  those  that  depress  the  lower  lip, 
the  lips  are  separated. 

8.  Muscle  that  draws  the  Lips  together. 

9.  Muscle  of  the  Temple  (Temporal  Muscle). 

10.  Masseter  Muscle.     9  and  10  are  the  two  chief  muscles  of  mastication,  for  when 
they  contract  the  movable  lower  jaw  is  elevated,  so  as  to  crush  the  food  between 
the  teeth  in  the  upper  and  lower  jaws. 

11.  Muscle  that  compresses  the  Nostril.     Close  to  its  outer  side  is  a  small  muscle 
that  dilates  the  nostril. 

12.  Muscle  that  wrinkles  the  Skin  of  the  Neck,  and  assists  in  depressing  the  lower 
jaw. 

13.  Muscle  that  assists  in  steadying  the  Head,  and  also  in  moving  it  from  side  to 
side. 

14.  Muscles  that  depress  the  Windpipe  and  Organ  of  Voice.    The  muscles  that  ele- 
vate the  same  parts  are  placed  beneath   the  lower  jaw,  and  cannot  be  seen  in 
the  figure. 

Muscles  that  connect  the  upper  extremity  of  the  trunk.  Portions  of 
four  of  these  muscles  are  represented  in  the  figure,  viz.  : 

15.  Muscle  that  elevates  the  Shoulder.     Trapezius  Muscle. 

17.  Great  Muscle  of  the  Chest,  which  draws  the  Arm  in  front  of  the  Chest  (Great 
Pectoral  Muscle). 

18.  Broad  Muscle  of  the  Back,  which  draws  the  Arm  downwards  across  the  back  of 
the  Body  (Latissimus  Dorsi). 

19.  Serrated  Muscle,  which  extends  between  the  Ribs  and  Shoulder  blade,  and  draws 
the  Shoulder  forwards  and  rotates  it,  a  movement  which  takes  place  in  the  ele- 
vation of  the  arm  above  the  head  (Serratus  magnus). 

At  a  lower  part  of  the  trunk,  on  each  side,  may  be  seen  the  large  muscle 
which,  from  the  oblique  direction  of  its  fibres,  is  called 
30.  Outer  Oblique  Muscle  of  the  Abdomen. 


EXPLANATION  OF  PLATE  II. 

Several  muscles  lie  beneath  it.     The  outline  of  one  of  these, 

21.  Straight  Muscle  of  the  Abdomen,  may  be  seen  beneath  the  expanded  tendon  of 
insertion  of  the  oblique  muscle.    These  abdominal  muscles,  by  their  contraction, 
possess  the  power  of  compressing  the  contents  of  the  abdomen. 

Muscles  of  the  upper  extremity  : 
16.  Muscle  that  elevates  the  Arm  (Deltoid  Muscle). 

22.  Biceps  or  Two-headed  Muscle  (see  also  page  55). 

23.  Anterior  Muscle  of  the  Arm.     This  and  the  Biceps  are  for  the  purpose  of  bend- 
ing the  Forearm. 

24.  Triceps,  or  Three-headed  Muscle.     This  counteracts  the  last  two  muscles,  for  it 
extends  the  Forearm. 

25.  Muscles  that  bend  the  Wrist  and  Fingers,  and  pronate  the  Forearm  and  Hand 
—that  is,  turn  the  Hand  with  the  palm  downwards.     They  are  called  the  Flexor 
and  Pronator  Muscles. 

26.  Muscles  that  extend  the  Wrist  and  Fingers,  and  supinate  the  Forearm  and  Hand 
— that  is,  turn  the  hand  with  its  palm  upwards.     They  are  called  the  Extensor 
and  Supinator  Muscles. 

ry.  Muscles  that  constitute  the  ball  of  the  thumb.     They  move  it  in  different  direc- 
tions. 

28.  Muscles  that  move  the  Little  Finger. 

Muscles  which  connect  the  lower  extremity  to  the  pelvic  bone  :  (Sev- 
eral are  represented  in  the  figure.) 

29.  Muscle  usually  stated  to  have  the  power  of  crossing  one  Leg  over  the  other, 
hence  called  the  Tailor's  Muscle,  or  Sartorius;  its  real  action  is  to  assist  in  bend- 
ing the  knee. 

30.  Muscles  that  draw  the  Thighs  together  (Adductor  Muscles). 

31.  Muscles  that  extend  or  straighten  the  Leg  (Extensor  Muscles).     The  muscles 
that  bend  the  Leg  are  placed  on  the  back  of  the  thigh,  so  that  they  cannot  be 
seen  in  the  figure. 

Muscles  of  the  leg  and  foot : 

32.  Muscles  that  bend  the  Foot  upon  the  Leg,  and  extend  the  Toes. 

33.  Muscles  that  raise  the  Heel — these  form  the  prominence  of  the  calf  of  the  Leg. 

34.  Muscles  that  turn  the  Foot  outwards. 

35.  A  band  of  Membrane  which  retains  in  position  the  tendons  which  pass  from  the 
leg  to  the  foot. 

36.  A  short  muscle  which  extends  the  Toes. 

The  muscles  which  turn  the  foot  inwards,  so  as  to  counteract  the  last- 
named  muscles,  lie  beneath  the  great  muscles  of  the  calf,  which  conse- 
quently conceal  them.  The  foot  possesses  numerous  muscles,  which  act 
upon  the  toes,  so  as  to  move  them  about  in  various  directions.  These  are 
principally  placed  on  the  sole  of  the  foot,  so  that  they  cannot  be  seen  in  the 
figure.  Only  one  muscle,  36,  which  assists  in  extending  the  toes,  is  placed 
on  the  back  of  the  foot. 


12 


36 


PLATE    II.— THE  SUPERFICIAL  MUSCLES  OF  THE   FRONT  OF  THE  BODY. 


MEAT  EXTRACTS.  63 

Liebig's  Extract  of  Meat  is  essentially  but  a  concentrated 
beef  tea ;  from  its  stimulating  effect  it  is  often  useful  to  per- 
sons in  feeble  health,  but  other  food  should  be  given  with  it. 
It  contains  all  the  flavoring  matters  of  the  meat,  and  its 
proper  use  is  for  making  gravies  and  flavoring  soups;  the 
erroneousness  of  the  common  belief  that  it  is  a  highly  nutri- 
tious food  cannot  be  too  strongly  insisted  upon,  as  sick  per- 
sons may  be  starved  on  it. 

Various  meat  extracts  are  now  prepared  by  subjecting  beef 
to  chemical  processes  in  which  it  undergoes  changes  like 
those  experienced  in  digestion.  The  myosin  is  thus  made 
soluble  in  water  and  uncoagulable  by  heat,  and  a  real  con- 
centrated meat  extract  is  obtained.  Before  relying  on  any 
one  of  them  for  the  feeding  of  an  invalid,  it  would,  however, 
be  well  to  insist  on  having  a  statement  of  its  method  of 
preparation,  and  then  to  consult  a  physician,  or  some  one 
else  who  has  the  requisite  knowledge,  in  order  to  ascertain  if 
the  method  is  such  as  might  be  expected  to  attain  the  end 
desired 


CHAPTER   VII. 
MOTION  AND   LOCOMOTION. 

The  Special  Physiology  of  Muscles.  — The  distinctive 
property  of  muscular  tissue  (i.e.,  its  power  of  contraction)  is 
everywhere  the  same ;  but  the  uses  of  different  muscles  are 
varied  by  reason  of  their  different  positions  and  mechanical 
condition.  Some  are  muscles  of  respiration,  others  of  swal- 
lowing;  some  bend  joints  and  are  called  flexors,  others 
straighten  them  and  are  called  extensors,  and  so  on.  The 
determination  of  the  exact  use  of  any  particular  muscle  is 
known  as  its  special  physiology,  as  distinguished  from  its  gen- 
eral physiology,  or  properties  as  a  muscle.  We  may  here 
consider  the  special  physiology  of  the  muscles  concerned  in 
standing  and  walking. 

Levers  in  the  Body. — In  nearly  all  cases  the  voluntary 
muscles  perform  their  work  with  the  co-operation  of  the 
skeleton.  When  muscles  move  bones  the  latter  are  to  be 
regarded  as  levers  whose  fulcra  lie  at  the  joint  where  the 
movement  takes  place.  Examples  of  the  three  forms  of 
levers  recognized  in  mechanics  are  found  in  the  human  body. 

Levers  of  the  First  Order. — In  this  form  (Fig.  40)  the 
fulcrum  or  fixed  supporting  point,  F,  lies  between  the  weight 
to  be  moved  and  the  moving  power.  The  distance  PF 
from  the  power  to  the  fulcrum  is  called  the  power-arm  of  the 
lever,  and  the  distance  WF  is  the  weight-arm.  When 

64 


LEYERS.  65 

power-arm  and  weight-arm  are  equal  (as  in  an  ordinary  pair 
of  scales)    no   mechanical   advantage   is   gained;    to  lift   a 


F 


FIG.  40. — A  lever  of  the  first  order.    F,  fulcrum  ;  P,  power  ;    W,  resistance  or 
weight. 

pound  at  W,  P  must  be  pressed  down  with  a  force  slightly 
greater  than  a  pound ;  and  the  end  W  will  go  up  just  as  far 
as  the  end  P  goes  down.  If  PF  be  longer  than  WF,  then  a 
small  weight  at  P  will  balance  a  larger  one  at  Wt  the  gain 
being  greater  the  greater  the  difference  in  the  length  of  the 
arms,  but  the  distance  through  which  W  is  moved  will  be 
less  than  that  through  which  P  moves ;  for  example,  if  PF  is 
twice  as  long  as  WF,  then  half  a  pound  at  P  will  balance  a 
pound  at  W,  and  a  little  more  than  half  a  pound  laid  on  the 
end  P  will  lift  a  pound  on  the  end  W,  but  W  will  only  go 
up  half  as  far  as  P  goes  down.  On  the  other  hand,  if  the 
weight-arm  is  longer  than  the  power-arm  there  will  be  a  loss 
in  force,  but  a  gain  in  the  distance  through  which  the  weight 
is  moved. 

An  example  of  levers  of  the   first  order  is  found  in  nod- 
ding movements  of  the  head,  the  fulcrum  being  where  the 


W 


FIG.  41. — A  lever  of  the  second  order.    F,  fulcrum  ;  P,  power  ;  W,  weight.     The 
arrows  indicate  the  direction  in  which  the  forces  act. 

occipital  bone  articulates   with  the  atlas  (Fig.    20).      When 
the  chin  is  raised  the  power  is  applied  to  the  skull  behind 


66  THE  HUMAN  BODY. 

the  fulcrum  by  muscles  passing  from  the  spinal  column  to 
the  back  of  the  head ;  the  resistance  to  be  overcome  is  the 
excess  in  weight  of  the  part  of  the  head  in  front  of  the  ful- 
crum over  that  behind  it,  and  is  not  great,  as  the  head  is 
nearly  balanced  on  the  top  of  the  spine.  To  let  the  chin 
drop  does  not  necessitate  any  muscular  effort. 

The  pull  of  the  triceps  to  straighten  the  arm,  and  of  the 
calf  muscles  in  rising  on  the  toes,  are  additional  examples  of 
the  action  of  levers  of  the  first  class ;  the  fulcrum  in  each 
case  is  at  the  joint,  as  it  is  in  all  the  lever  systems  of  the 
body. 

Levers  of  the  Second  Order. — In  this  form  of  lever  (Fig. 
41)  the  weight  or  resistance  acts  between  the  fulcrum  and 
the  power.  The  power-arm,  PF,  is  accordingly  always  longer 
than  the  weight-arm,  WF,  and  so  a  comparatively  weak 
force  can  overcome  a  considerable  resistance.  There  is, 
however,  a  loss  in  rapidity  and  extent  of  movement,  since 
it  is  obvious  that  when  P  is  raised  a  certain  distance  W  will 
be  raised  less.  Levers  of  this  class  are  practically  unknown 
in  muscular  action. 

Levers  of  the  Third  Order. — In  these  (Fig.  42)  the 
power  is  applied  between  the  fulcrum  and  the  weight ;  hence 
the  power-arm,  PF,  is  always  shorter  than  the  weight-arm, 


W  F 

FIG.  42. — A  lever  of  the  third  order.     F^  fulcrum  ;  P,  power  ;   W,  weight. 

WF.     The  moving  force  acts  at  a  mechanical  disadvantage, 
but  swiftness  and  range  of  movement  are  gained.     This  is  the 


PULLEYS  IN   THE  BODY— STANDING.  67 

form  of  lever  most  commonly  used  in  the  body.  For  exam- 
ple, when  the  forearm  is  bent  up  towards  the  arm,  the 
fulcrum  is  the  elbow  joint  (Fig.  31);  the  power  is  applied  at 
the  insertion  of  the  biceps  muscle  into  the  radius  ;  the  weight 
is  that  of  the  forearm  and  hand  and  whatever  may  be  held  in 
the  latter,  and  acts  at  the  centre  of  gravity  of  the  whole, 
somewhere  on  the  far  side  of  the  point  of  application  of  the 
power.  Usually  (as  in  this  case)  the  power-arm  is  very 
short,  so  as  to  gain  speed  and  extent  of  movement,  the  mus- 
cles being  strong  enough  to  work  at  a  considerable  me- 
chanical disadvantage.  The  limbs  are  thus  also  made  much 
more  shapely  than  would  be  the  case  were  the  power  applied 
near  or  beyond  the  weight. 

Pulleys  in  the  Body. — Fixed  pulleys  are  used  in»the 
body ;  they  give  rise  to  no  loss  or  gain  of  power,  but  serve 
to  change  the  direction  in  which  certain  muscles  pull.  One 
of  the  muscles  of  the  eyeball,  for  example,  has  its  origin  at 
the  back  of  the  eye  socket,  from  there  it  passes  to  the  front 
and  ends  in  a  long  tendon,  before  it  reaches  the  eyeball. 
This  tendon  passes  through  a  ring  attached  to  the  margin  of 
the  frontal  bone,  and  then  turns  back  to  its  insertion  on  the 
eyeball.  The  direction  in  which  the  muscle  moves  the  eye 
is  thus  quite  different  from  what  it  would  be  if  the  tendon 
went  directly  to  the  eyeball. 

Standing. — We  slowly  learn  to  stand  in  the  first  year  after 
birth,  and  though  we  finally  come  to  do  it  without  conscious 
attention,  standing  always  requires  the  co-operation  of  many 
muscles,  guided  and  controlled  by  the  nervous  system.  The 
influence  of  the  latter  is  shown  by  the  fall  following  a  severe 
blow  on  the  head,  which  has  fractured  no  bone  and  injured 
no  muscle;  "the  concussion  of  the  brain  "  stuns  the  man, 
and  until  it  has  passed  off  he  cannot  stand. 


68  THE  HUMAN  BODY. 

When  we  stand  erect,  with  the  arms  close  by  the  sides  and 
the  feet  together,  the  centre  of  gravity  of  the  whole  adult  body 
lies  at  the  articulation  between  the  sacrum  and  the  last  lumbar 
vertebra,  and  a  vertical  line  drawn  from  it  will  reach  the 
ground  between  the  feet.  In  any  position  in  which  this  vertical 
falls  within  the  space  bounded  by  a  line  drawn  close  around 
both  feet,  we  can  stand.  When  the  feet  are  together  the  area 
enclosed  by  this  line  is  small,  and  a  slight  sway  of  the  trunk 
will  throw  the  centre  of  gravity  of  the  body  outside  it ;  the 
more  one  foot  is  in  front  of  the  other,  the  greater  the  sway 
back  or  forward  which  will  be  compatible  with  safety,  and  the 
greater  the  lateral  distance  between  the  feet,  the  greater  the 
lateral  sway  which  is  possible  without  falling.  Consequently, 
when  a  man  wants  to  stand  very  firmly  he  advances  one  foot 
obliquely,  so  as  to  increase  his  base  of  support  in  both  direc- 
tions. 

In  consequence  of  the  flexibility  of  its  joints  a  dead  body 
cannot  be  balanced  on  its  feet  as  a  statue  can.  When  we 
stand,  the  ankle,  knee,  and  hip  joints,  if  not  braced  by  the 
muscles,  give  way,  and  the  head  also  falls  forward  on  the 
chest.  But  (Fig.  43)  muscles  (i)  in  front  of  the  ankle  joint, 
and  others  (I)  behind  it,  by  contracting  at  the  same  time, 
keep  the  joint  from  yielding ;  similarly  the  contraction  of 
muscles  (2)  in  front  of  the  knee  and  hip  joints,  with  their  an- 
tagonists (II),  make  these  joints  rigid ;  in  like  manner,  the 
muscles  (III)  which  run  from  the  pelvis  to  the  back  of  the  head 
pull  against  those  (3  and  4)  which  run  from  the  pelvis  to  the 
lower  end  of  the  breastbone,  and  from  the  upper  end  of  the 
breastbone  to  the  anterior  part  of  the  skull,  and  their  bal- 
anced contraction  keeps  the  head  erect.  Since  the  degree 
to  which  each  muscle  concerned  contracts  when  we  stand  must 
be  accurately  adjusted  to  the  contraction  of  its  antagonist 


WALKING. 


69 


on  the  opposite  side  of  the  joint,  we  may  easily  comprehend 
why  it  takes  us  some  time  to  learn  to  stand,  and  why  a  stunned 
man,  whose  muscles  have  lost  guidance 
from  the  nervous  system,  falls. 

Locomotion  includes  all  movements  of 
the  body  in  space,  dependent  on  its  own 
unaided  muscular  efforts,  such  as  walking, 
running,  leaping,  and  swimming. 

Walking. — In  walking,  the  heel  of  the 
advanced  foot  reaches  the  ground  before 
the  toe  of  the  rear  foot  has  been  raised 
from  it.  In  each  step  the  advanced  leg 
supports  the  body,  and  the  rear  foot 
propels  it. 

A  little  attention  will  enable  any  one 
to  analyze  the  act  of  walking  for  himself. 
Stand  with  the  heels  together  and  take 
a  step,  commencing  with  the  left  foot.  The 
whole  body  is  at  first  inclined  forwards, 
the  movement  taking  place  mainly  at 
the  ankle  joints.  This  throws  the  centre 
of  gravity  in  front  of  the  base  formed  by 
the  feet,  and  a  fall  would  result  were 
not  the  left  foot  simultaneously  raised  by 

FIG.  43. — Diagram  illus- 

bending;  the  knee  a  little,  and  swung  for-  trating  the  muscles  (drawn 

in       thick       black       lines) 

wards,  the  toes  just  clear  of  the  ground  and 
the  sole  nearly  parallel  to  it.  When  the 
step  is  completed  the  left  knee  is  straight- 
ened and  the  foot  placed  on  the  ground,  the  heel  touching 
first ;  the  base  is  thus  extended  in  the  direction  of  the 
stride  and  the  fall  prevented.  Meanwhile  the  right  leg 
is  kept  straight  but  inclined  forwards,  carrying  the  trunk 


i 


their      balanced      activity 

keep  the  joints  rigid  and 

the  body  erect. 


70  THE  HUMAN  BODY. 

during  the  step  while  the  left  foot  is  off  the  ground ;  the 
right  foot  is  now  raised,  commencing  with  the  heel,  and 
when  the  step  of  the  left  leg  is  completed,  only  the  great 
toe  of  the  right  is  in  contact  with  the  support.  With 
this  toe  a  push  is  given  which  sends  the  body  swinging  for- 
ward, supported  on  the  left  leg,  which  now  in  turn  is  kept 
rigid  except  at  the  ankle  joint ;  the  right  knee  is  immedi- 
ately bent  and  that  leg  swings  forwards,  its  foot  just  clear  of 
the  ground,  as  the  left  did  before.  The  body  meanwhile  is 
supported  on  the  left  leg  alone.  When  the  right  leg  com- 
pletes its  step  its  knee  is  straightened  and  the  foot  thus 
brought,  heel  first,  on  the  ground  ;  while  it  is  swinging  for- 
wards the  left  heel  is  gradually  raised,  and  at  the  end  of  the 
step  the  great  toe  alone  is  on  the  ground ;  with  this  a  push  is 
given  as  was  the  case  with  the  right  foot,  and  the  left  leg 
then  swings  forward  to  make  the  next  step.  Walking  may, 
in  fact,  be  briefly  described  as  the  act  of  continually  falling 
forward  and  preventing  the  completion  of  the  fall  by  thrust- 
ing out  a  leg  to  meet  the  ground  in  front. 

During  each  step  the  body  sways  a  little  from  side  to  side, 
as  it  is  alternately  borne  by  the  right  and  left  legs.  It  also 
sways  up  and  down  a  little ;  a  man  standing  with  his  heels 
together  is  taller  than  when  standing  with  one  foot  advanced, 
just  as  a  pair  of  compasses  held  erect  on  its  points  is  higher 
when  its  legs  are  together  than  when  they  are  apart.  In  that 
period  of  each  step  when  the  advancing  trunk  is  balanced 
vertically  over  one  leg,  the  walker's  trunk  is  more  elevated 
than  when  the  front  foot  also  is  on  the  ground.  Women, 
accordingly,  often  find  that  a  dress  which  clears  the  ground 
when  they  are  standing  sweeps  the  pavement  when  they 
walk. 

The  length  of  each  step  is  primarily  dependent  on  the 


HYGIENE  OP  THE  MUSCLES.  *Ji 

length  of  the  legs,  though  it  can  be  controlled  by  muscular 
effort ;  this  control  we  see  in  a  regiment  of  soldiers,  all  of 
whom  have  been  taught  to  take  the  same  stride,  no  matter 
low  their  legs  vary  in  length.  In  natural  easy  walking,  little 
muscular  effort  is  employed  to  carry  the  rear  leg  forward 
after  it  has  given  its  push;  it  swings  on  like  a  pendulum 
when  its  foot  is  clear  of  the  ground.  As  short  pendulums 
swing  faster  than  long  ones  the  natural  step  of  short-legged 
people  is  quicker  than  that  of  long-legged. 

Running  differs  from  walking  in  several  respects.  There 
is  a  moment  when  both  feet  are  off  the  ground;  the  toea 
alone  come  in  contact  with  it  at  each  step ;  and  the  knee 
joint  is  not  straight  at  the  end  of  the  step.  In  running, 
when  the  rear  foot  is  to  leave  the  ground  the  knee  is  sud- 
denly straightened  and  the  ankle  joint  extended  so  as  to  push 
the  toes  forcibly  on  the  ground  and  powerfully  impel  the 
whole  body  forwards  and  upwards.  The  knee  is  then  flexed 
and  the  foot  raised  before  the  toes  of  the  front  foot  reach  the 
ground.  In  each  step  the  raised  leg  is  forcibly  drawn  for- 
ward and  not  allowed  to  swing  passively  as  in  quiet  walking. 
This  increases  the  rate  at  which  the  steps  follow  one  another, 
and  the  one-legged  jump  that  occurs  through  the  jerk  given 
by  the  straightening  knee  of  the  rear  leg,  just  before  it  leaves 
the  ground,  increases  the  distance  covered  at  each  step. 

Hygiene  of  the  Muscles. — The  healthy  working  of  the 
muscles  is  dependent  on  a  healthy  state  of  the  body  in  gen- 
eral. Hence  good  food  and  pure  air  are  necessary  for  a 
vigorous  muscular  system.  Muscles  also  should  not  be  ex~ 
posed  to  any  considerable  continued  pressure,  since  this  in- 
terferes with  the  flow  of  the  blood  and  lymph  essential  for 
their  nutrition. 

Exercise    is    necessary   for   the    best  development    of  the 


72  THE  HUMAN  BODY. 

muscles.  A  muscle  long  left  unused  diminishes  in  bulk  and 
degenerates  in  quality,  as  is  well  seen  when  a  muscle  is  para- 
lyzed and  remains  permanently  inactive  because  of  injury  to 
its  nerve ;  although  at  first  the  muscle  itself  may  be  perfectly 
healthy,  it  alters  in  a  few  weeks,  and  when  the  nerve  is  re- 
paired the  muscle  may  be  incapable  of  activity.  The  same 
fact  is  illustrated  by  the  feeble  and  wasted  state  of  the  mus- 
cles of  a  limb  which  has  been  kept  motionless  in  splints  for  a 
long  time ;  when  the  splints  are  removed,  it  is  only  after 
careful  and  persistent  exercise  that  the  long  idle  muscles 
regain  their  former  size  and  power.  The  great  muscles  of 
the  "brawny  arm"  of  the  blacksmith  illustrate  the  converse 
fact — the  growth  of  muscles  when  exercised. 

Exercise,  to  be  useful,  must  be  judicious ;  taken  to  the 
point  of  extreme  fatigue,  day  after  day,  it  may  do  harm. 
When  a  muscle  is  worked  some  of  its  substance  is  used  up ; 
at  the  same  time  and  afterwards  more  blood  flows  to  it,  and 
if  the  exercise  is  not  too  violent  and  the  intervals  of  rest  are 
long  enough,  the  repair  and  growth  will  keep  pace  with  or 
exceed  the  wasting,  but  excessive  work  and  too  short  rest 
like  too  little  exercise  may  lead  to  diminution  and  enfeeble- 
ment  of  the  muscle. 

Few  persons  can  profitably  attempt  to  work  hard  daily 
with  both  brain  and  muscle,  but  all  should  regularly  use 
both,  choosing  which  to  work  with,  and  which  merely  to 
exercise  The  best  earthly  life,  that  of  the  healthy  mind  in 
the  healthy  body,  can  only  so  be  attained.  For  persons  of 
average  physique,  engaged  in  study  or  business  pursuits  of  a 
sedentary  nature,  the  minimum  of  daily  exercise  should  be 
an  amount  equivalent  to  a  five  or  an  eight  mile  walk. 

Time  for  Exercise. — Since  extra  muscular  work  means 
extra  muscular  waste,  and  should  be  accompanied  by  an 


VARIETIES  OF  EXERCISE.  73 

abundant  supply  of  food  materials  to  the  muscles,  violent 
exercise  should  not  be  taken  after  a  long  fast.  Neither 
should  it  be  taken  immediately  after  a  meal ;  a  great  deal  of 
blood  is  then  needed  in  the  digestive  organs  to  provide  ma- 
terials for  digesting  the  food,  and  this  blood  cannot  be  sent 
off  to  the  muscles  without  the  risk  of  an  attack  of  indiges- 
tion. Strong  and  hearty  young  people  may  take  a  long 
walk  before  breakfast,  but  others  should  wait  until  after 
eating  before  engaging  in  any  kind  of  hard  work. 

Varieties  of  Exercise. — In  walking  and  running  the  mus- 
cles of  the  lower  limbs  and  trunk  are  chiefly  used,  whereas 
the  muscles  of  the  chest  and  arms  are  not.  Rowing  is  better, 
since  in  it  nearly  all  the  muscles  are  active.  No  one  exercise 
employs  in  proper  proportion  all  the  muscles,  and  gymnasia 
in  which  different  feats  of  agility  are  practised  so  as  to  call 
different  muscles  into  action  have  a  deserved  popularity.  It 
should  be  borne  in  mind,  however,  that  the  legs  especially 
need  strength,  whereas  the  arms  need  delicacy  of  control 
rather  than  great  strength.  Out-of-door  exercise  in  good 
weather  is  better  than  any  other,  and  every  one  can  at  least 
take  a  walk.  The  daily  "constitutional"  is  very  apt  to 
become  wearisome,  especially  to  young  persons,  and  exer- 
cise loses  half  its  value  if  unattended  with  feelings  of  mental 
relaxation  and  pleasure.  Active  games,  for  this  reason, 
have  a  great  value  for  young  and  healthy  persons ;  'bicycling, 
golf,  lawn-tennis,  baseball,  and  cricket  are  all  attended  with 
pleasurable  excitement,  and  are  excellent  as  exercising  many 
muscles.  Such  exercises  as  make  one  breathe  faster  and 
deeper  and  increase  the  rapidity  and  force  of  the  pulse  are 
excellent  for  giving  exercise  to  the  heart  and  training  the 
respiratory  and  circulatory  nerve  centres.  The  lungs  and 
chest  are  also  developed  thereby. 


CHAPTER   VIII. 
WHY  WE  EAT  AND   BREATHE. 

How  is  it  that  the  Body  can  Do  Muscular  Work  ? — In 
the  muscles  we  possess  a  set  of  organs  capable  of  moving  the 
body  from  place  to  place,  of  changing  the  relative  positions 
of  its  parts,  and  of  lifting  external  objects  ;  as  long  as  we  are 
alive,  some  of  our  muscles  are  at  each  moment  doing  me- 
chanical work.  This  fact  suggests  the  question,  where  does 
this  power  of  working  come  from  ?  % 

The  Conservation  of  Energy.  —  The  different  natural 
forces  known  to  us  are  not  nearly  so  numerous  as  the  chemical 
elements ;  we  all,  however,  know  several  of  them,  as  light, 
heat,  electricity,  and  mechanical  work.  One  of  the  greatest 
discoveries  of  the  nineteenth  century  is  that  these  different 
natural  forces,  or  forms  of  energy,  can  be  turned  one  into 
another,  directly  or  indirectly.  Kinds  of  energy  are  trans- 
mutable,  while,  so  far  as  we  know  at  present,  kinds  of  mat- 
ter are  not.  We  cannot,  as  the  alchemists  hoped,  turn  iron 
or  mercury  into  gold,  but  we  can  turn  heat  into  light,  into 
electrical  force,  or  into  mechanical  work.  When  such  trans- 
formations are  made  it  is  always  found  that  a  definite  amount 
of  one  kind  of  energy  disappears  to  give  rise  to  a  definite 
amount  of  another.  In  other  words,  it  has  been  discovered 
that  energy  cannot  be  created.  If  we  take  a  given  quantity 
of  heat  we  can  turn  it  into  mechanical  work ;  if  we  then 

74 


THE  CONSERVATION  OF  ENERGY.  75 

turn  all  this  mechanical  work  back  into  heat  we  get  again 
exactly  the  quantity  of  heat  which  disappeared  when  the 
mechanical  work  appeared,  and  so  with  all  other  transforma- 
tions of  energy  from  one  kind  to  another  and  back  again. 
This  fact  that  energy  or -work-power  can  be  turned  from  one 
kind  into  another,  and  often  back  again,  but  never  created  from 
nothing  or  finally  destroyed,  is  known  as  the  law  of  the  con- 
servation of  energy. 

Illustrations  of  the  Conservation  of  Energy. — In  a  steam- 
engine,  heat,  which  is  the  best  known  kind  of  energy,  is  pro- 
duced in  the  furnace.  When  the  engine  is  at  work  all  of  this 
energy  does  not  leave  it  as  heat ;  some  is  turned  into  me- 
chanical work,  and  the  more  work  the  engine  does  the  greater 
is  the  difference  between  the  heat  generated  in  the  furnace 
and  that  leaving  the  machine.  If,  however,  we  use  the  work 
to  rub  two  rough  surfaces  together  we  can  get  the  heat  back, 
and  if  (which  of  course  is  impossible  in  practice)  *  we  could 
avoid  all  friction  between  the  moving  parts  of  the  machine, 
and  have  all  parts  of  the  engine  at  the  end  of  the  experiment 
at  exactly  the  same  temperature  as  at  the  beginning,  the 
quantity  of  heat  obtained  plus  the  quantity  which  has  been 
carried  off  from  it  by  the  air  since  its  fires  were  lighted 
would  be  exactly  equal  to  the  amount  of  heat  originally  gen- 
erated in  the  furnace  of  the  engine.  Having  turned  some  of 
the  heat  into  mechanical  work  we  could  thus  turn  the  work 
back  into  heat  again,  and  find  it  yield  exactly  the  amount 
which  seemed  lost. 

Or  we  might  use  the  engine  to  drive  an  electro-magnetic 
machine  and  so  turn  part  of  the  heat  liberated  in  its  furnace, 

*  The  losses  of  heat  through  radiation  and  the  heating  of  the  air,  and 
the  losses  of  mechanical  energy  by  friction  between  the  parts  of  ma- 
chines, are  great  and  constantly  diminish  the  supply  of  force. 


76  THE  HUMAN  BODY. 

first  into  mechanical  work,  and  this  afterwards  into  elec- 
tricity ;  and  if  we  choose  to  use  the  latter  with  the  proper 
apparatus,  as  now  used  for  electric  lighting,  we  can  turn 
more  or  less  of  it  into  light,  and  so  have  a  great  part  of  the 
energy  which  first  became  conspicuous  as  heat  in  the  engine 
furnace,  now  manifested  in  the  form  of  light  at  some  distant 
point.  In  theory,  starting  with  a  given  quantity  of  one  kind 
of  energy,  we  may  turn  it  into  one  or  more  other  forms ;  but 
if  we  collect  all  the  final  forms  and  retransform  them  into  the 
first,  we  shall  have  exactly  the  amount  of  it  which  disap- 
peared when  the  other  kinds  appeared. 

Why  We  Need  Food. — Energy,  as  we  have  seen,  cannot 
be  created  from  nothing ;  since  the  body  constantly  expends 
energy,  it  must  have  a  steady  supply.  This  supply  comes 
from  the  energy  liberated  when  substances  in  the  body  are 
burned,  or,  as  the  chemists  say,  oxidized,  just  as  that  used  by  a 
locomotive  comes  from  the  burning  or  oxidation  of  coal  or 
wood  in  its  furnace.  In  consequence  of  this  constant  oxida- 
tion, new  materials  must  constantly  be  supplied  to  make  up 
for  those  used  for  oxidation.  These  new  materials  are  pro- 
vided in  our  food.  One  chief  reason  for  eating  is  that  we 
may  replace  the  material  which  has  been  burned  to  set  free 
the  energy  needed  for  our  muscular  efforts. 

Why  the  Body  is  Warm. — Keeping  warm  is  a  very  im- 
portant matter,  for  experiment  shows  that  no  tissue  of  the 
human  body  works  well  when  cooled  down  even  a  few  de- 
grees below  98.5°  F.,  its  natural  healthy  temperature.  Care- 
ful experiments  prove  that  when  a  muscle  works  it  becomes 
hotter,  and  we  all  know  that  exercise  makes  us  warm.  This 
shows  that  the  oxidation  which  takes  place  in  a  working 
muscle  is  not  all  turned  into  mechanical  work,  but  a  good 
share  of  it  appears  as  heat.  What  is  true  of  muscle  is  true  of 


THE  NECESSITY  OF  FOOD.  77 

all  other  organs  of  the  body  when  they  work.  No  matter 
what  their  kind  of  work,  material  is  oxidized,  and  some  of 
the  energy  set  free  by  the  oxidation  appears  as  heat,  assist- 
ing to  keep  the  body  warm  and  at  its  best  working  tempera- 
ture. 

A  Second  Beason  Why  We  Need  Food. — Since  the  body 
works  best  at  a  temperature  higher  than  that  of  the  surround- 
ing air  (except  on  a  very  hot  day),  and  in  health  always 
keeps  at  this  temperature,  it  must  lose  heat  nearly  all  the 
time.  At  night  each  of  us  is,  in  health,  just  as  warm  as  in  the 
morning,  and  in  the  morning  as  when  we  went  to  bed, 
though  we  have  lost  heat  to  the  air  during  the  day,  and  to  the 
bedclothes  at  night.  In  order  to  keep  our  bodies  at  the  tem- 
perature most  suitable  to  their  activity,  they  must,  therefore, 
generate  heat  all  the  time,  to  compensate  for  its  continued 
loss.  In  this  necessity  of  generating  heat  we  find  a  second 
reason  for  taking  food. 

The  Influence  of  Starvation  upon  Muscular  Work  and 
Animal  Heat. — The  body  does  not  live,  work,  and  keep 
warm  by  means  of  any  peculiar  vital  force  or  energy  which 
inhabits  it,  but  by  utilizing  the  energy  set  free  in  it  by  the 
oxidation  of  foods,  or  of  substances  made  in  it  from  foods. 
When  a  man  is  deprived  of  food,  the  supply  of  material  for 
oxidation  is  cut  off;  the  body  first  uses  up  any  reserve  of 
nutritious  matter  which  may  have  been  stored  up  in  it  when 
the  starvation  commenced,  then  the  tissues  are  attacked,  and 
as  they  are  burned  up  the  body  becomes  weaker  and  weaker 
until  death  supervenes.* 

*  When  warm-blooded  animals  are  starved  their  temperature  slowly 
falls;  and  when  it  comes  down  to  about  77°  F.  (25°  C.)  death  occurs.  The 
various  tissues  at  that  temperature  can  no  longer  work  so  as  to  maintain 
life. 


7*  THE  HUMAN  BODY. 

How  long  a  man  totally  deprived  of  food  can  keep  alive 
depends  partly  on  how  much  reserve  material,  capable  of  ox- 
idation, he  has  stored  up  in  him  when  the  starvation  period 
commences ;  but  largely,  also,  on  the  extent  to  which  he  can 
avoid  muscular  work  and  loss  of  heat.  The  breathing  move- 
ments and  beat  of  the  heart  must  go  on,  but  if  the  individual 
lies  quiet  in  bed  he  need  do  little  or  no  other  muscular  work  ; 
and  if  he  is  well  covered  up  with  blankets,  the  loss  of  heat 
from  the  body  is  slight  and  calls  for  but  little  oxidation  of  the 
tissues  to  compensate  for  it.*  Also,  a  healthy  fat  person  will 
survive  starvation  longer  than  a  healthy  lean  one  ;  during  the 
process  his  fat  is  slowly  burnt ;  but  so  long  as  it  lasts  he  can 
supply  his  muscles  with  something  which  can  be  oxidized  to 
yield  working  power  and  maintain  his  temperature.  Fat  is, 
in  fact,  a  sort  of  reserve  fuel,  laid  up  in  the  body,  and  one 
can  hardly  be  said  to  begin  to  starve  until  his  fat  -has  nearly 
all  been  used  up.f 

Oxidations  in  the  Body. — In  the  preceding  paragraphs 
oxidation  and  burning  have  been  used  as  equivalent  phrases, 
in  accordance  with  the  teachings  of  chemistry.  To  the 
chemist  a  substance  is  burned  when  it  is  combined  with 

*  Hence  Dr.  Tanner  and  "fasting  girls"  keep  in  bed,  warmly  cov- 
ered up,  most  of  the  time.  The  losses  of  the  body  in  mechanical  work  and 
heat  are  thus  reduced  to  a  minimum,  and  consequently  the  oxidation  of 
the  food  reserves  stored  in  the  body  at  the  beginning  of  the  fast. 

f  Some  warm-blooded  animals,  as  bears,  hibernate,  that  is,  sleep  all 
through  the  winter  and  take  no  food.  They  feed  well  in  the  warm 
weather,  and  are  quite  fat  at  the  close  of  autumn,  when  they  seek  some 
sheltered  place  to  winter  in.  This  shelter  and  their  warm,  furry  coats 
make  the  loss  of  heat  very  little;  the  animal,  except  for  its  breathing  and 
the  beat  of  its  heart,  hardly  ever  moves  during  the  winter,  and  even  those 
necessary  movements  are  reduced  to  the  fewest  possible,  the  breathing 
and  heart  beat  being  much  slower  than  during  the  summer.  With  return 
of  warm  weather  the  creature  wakes  up  again,  but  is  then  lean  and  weak, 
having  burnt  up  its  fat  and  part  of  its  muscle  during  its  winter  sleep. 


OXIDATIONS  IN  THE  BODY.  79 

oxygen,  whether  this  combination  takes  place  slowly  or 
rapidly.  If  the  combination  occurs  rapidly,  the  burning  or 
oxidizing  mass  becomes  very  hot  and  also  gives  off  light. 
Such  a  rapid  and  vigorous  oxidation  is  called  a  combustion;  no 
combustions  take  place  in  our  bodies. 

It  has,  however,  been  proved  that  whether  the  combination 
of  oxygen  with  an  oxidizable,  or  burnable,  substance  takes  place 
rapidly  or  slowly,  at  the  end  of  the  process  exactly  the  same 
amount  of  energy  will  have  been  set  free  in  each  case.  When 
the  oxidation  occurs  in  a  'few  seconds,  the  oxidizing  mass  be- 
comes very  frot ;  when  it  occurs  slowly,  in  a  few  days  or 
weeks,  the  mass  will  never  be  very  hot,  because  the  heat 
set  free  in  the  process  is  carried  off  nearly  as  fast  as  it 
appears. 

Illustrations  of  Oxidations  at  a  Low  Temperature. — If  a 
piece  of  magnesium  wire  be  ignited  in  the  air,  it  will  become 
white-hot,  flame,  and  leave  at  the  end  of  a  few  seconds  only  a 
certain  amount  of  incombustible  rust  or  magnesia,  which  con- 
sists of  the  metal  combined  with  oxygen  ;  under  these  circum- 
stances it  has  been  burnt  or  oxidized  quickly  at  a  high 
temperature.  The  heat  and  light  evolved  in  the  process  rep- 
resent the  energy  which  is  set  free  by  the  union  of  the  metal 
and  oxygen.  We  can,  however,  oxidize  the  metal  in  a  dif- 
ferent way.  If,  for  instance,  we  leave  it  in  damp  air,  it  will 
be  gradually  turned  into  magnesia  without  having  ever  been 
hot  to  the  touch  or  luminous  to  the  eye.  The  process  then, 
however,  takes  days  or  weeks,  but  in  this  slow  oxidation  just 
as  much  energy  is  liberated  as  in  the  former  case,  although 
now  all  takes  the  form  of  heat.  The  slowly  oxidizing  magne- 
sium is,  in  consequence,  at  no  moment  noticeably  hot,  since 
it  loses  its  heat  to  surrounding  objects  as  fast  as  it  generates  it. 
The  oxidations  occurring  in  our  bodies  are  of  this  slow  kind. 


8o  THE  HUMAN  BODY. 

An  ounce  of  arrowroot  oxidized  in  a  fire  liberates  exactly 
as  much  energy  as  if  burned  in  the  body,  but  the  oxidation 
takes  place  in  a  shorter  time  and  at  a  much  higher  tempera- 
ture. 

Oxidation  in  the  Presence  of  Moisture. — Wet  wood  or 
wet  coal  we  know  will  not  burn  easily,  but  other  kinds  of  ox- 
idation which  take  place  in  the  presence  of  moisture  are  well 
known.  The  rusting  of  iron,  for  example,  is  an  oxidation  of 
the  metal,  and  takes  place  faster  in  damp  air  than  in  dry ; 
during  the  slow  rusting  in  moisture  just  as  much  heat  is  set 
free  as  if  the  same  compound  of  iron  and  oxygen  were  pre- 
pared in  a  more  rapid  way.  Such  experiments  throw  great 
light  on  the  oxidations  which  take  place  in  our  own  bodies.  All 
of  them  are  slow  oxidations,  which  never  at  any  one  moment 
give  off  a  great  amount  of  heat,  and  all  occur  in  the  wet 
tissues. 

Summary : 

(1)  The  body  is  enabled  constantly  to  expend  energy  in 
muscular  work  and  in  heat  only  because  the  law  of  the  con- 
servation of  energy  is  operative  here  as  elsewhere  in  nature's 
dominions. 

( 2 )  This  law   is :    Energy  can  be  transformed  from  one 
kind   to  another,    but   can   never  be  created  from  nothing, 
increased,  diminished,  nor  finally  destroyed. 

(3)  In  accordance  with  this  law  the  energy  expended  by 
the  body  must  have  a  source. 

(4)  Investigations  have  shown  that  the  source  of  the  body's 
energy  is  found  in  the  oxidation  of  materials. 

(  5  )  Such  oxidizable  materials  are  furnished  by  food,  which 
includes  not  only  that  taken  into  the  body  at  any  time,  but 
storage  substance,  such  as  fat. 

(6)   Rapid  and  vigorous  oxidation  is  combustion. 


THE  OXYGEN  FOOD  OF  THE  BODY.       Si 

(7)  The  same  amount  of  energy  is  liberated  whether  the 
oxidation  is  slow  or  rapid. 

(8)  In  the  body  oxidation  is  always  relatively  slow,  and 
takes  place  in  the  presence  of  moisture. 

(9)  Hence,  by  the  transformation  of  energy  through  oxi- 
dation in  the  body  of  the  materials  furnished  by  food,  the 
body  is  enabled  to  expend  (#)  muscular  energy,  whereby  its 
work  is  accomplished ;  and  (£)  heat,  whereby  its  tissues  are 
kept  at  their  best  working  temperature  and  the  constant  outgo 
of  heat  compensated. 

The  Oxygen  Food  of  the  Body. — Hitherto  we  have  con- 
sidered the  energy  supply  of  the  body  only  from  one  side  ;  we 
have  regarded  it  as  dependent  on  the  constant  supply  of 
oxidizable  material.  But  this  is  only  half  the  question,  since 
if  substances  are  to  be  oxidized  there  must  be  a  provision  of 
oxygen  to  oxidize  them. 

In  order  that  a  steam-engine  may  work  and  keep  warm  it  is 
not  merely  necessary  that  it  have  plenty  of  coal,  but  it  must 
also  have  a  draught  of  air  through  its  furnace.  Chemistry 
teaches  us  that  the  burning  in  this  case  consists  in  the  combi- 
nation of  a  gas  called  oxygen,  taken  from  the  air,  with  carbon 
and  hydrogen  in  the  coals  ;  when  this  combination  takes 
place  a  great  deal  of  heat  is  given  off.  The  same  thing  is 
true  of  our  bodies.  In  order  that  food  matters  may  be  burnt 
in  them  and  enable  us  to  work  and  keep  warm,  they  must  be 
supplied  with  oxygen  ;  this  they  get  from  the  air  by  breathing. 
We  all  know  that  if  the  supply  of  air  be  cut  off,  a  man  will  die 
in  a  few  minutes  ;  his  food  is  no  use  to  him  unless  he  gets 
oxygen.  While  he  usually  has  stored  up  in  his  body  an  ex- 
cess oifood  matters,  he  has  little  or  no  reserve  of  oxygen.  In 
ordinary  language  we  do  not  call  oxygen  a  food,  but  restrict 
that  name  to  the  solids  and  liquids  which  we  swallow ;  but 


82  THE  HUMAN  BODY. 

inasmuch  as  it  is  a  material  which  we  must  take  from  the 
external  universe  into  our  bodies  to  keep  us  alive,  oxygen  is 
really  a  food.  Suffocation,  as  death  from  deficient  air  supply 
is  named,  is  really  death  from  oxygen  starvation. 


CHAPTER  IX. 
NUTRITION. 

The  Wastes  of  the  Body. — A  man  takes  into  his  body 
daily  several  pounds  of  foods  of  various  kinds,  as  meats, 
bread,  vegetables,  and  water,  yet  he  grows  no  heavier.  It  is, 
therefore,  clear  that  his  body  must  in  every  twenty-four  hours 
return,  on  the  average,  to  the  outside  world  about  as  great  a 
weight  of  matter  as  it  receives  from  it.  Even  in  childhood, 
while  growth  is  taking  place  and  the  body  becoming  heavier, 
the  gain  is  always  much  less  than  the  weight  of  the  foods 
swallowed.  The  materials  given  off  daily  from  the  body, 
which  balance  more  or  less  accurately  the  receipts  from  the 
outside  world,  are  its  wastes,  and  are  chiefly  things  which 
cannot  be  burned.  Much  of  the  food  taken  in  can  be,  and 
is,  oxidized  to  enable  us  to  move  and  keep  warm.  When 
burned  it  is  of  no  further  use  to  us,  and  would  only  clog  up 
the  various  organs,  as  the  ashes  and  smoke  of  an  engine 
would  soon  put  out  its  fire  if  they  were  allowed  to  accumulate 
in  the  furnace.  The  chief  wastes  *  of  the  body  are  carbon 
dioxide  gas,  water,  and  a  substance  related  to  ammonia  called 
urea. 

*  Chemically  these  wastes  are  : 

Carbon  dioxide  =  CO2 
Water  =  H2O 

Urea  =  CON2H4. 

83 


4  THE  HUMAN  BODY. 

Receptive  and  Excretory  Organs. — Those  organs  of  the 
body  whose  function  it  is  to  gather  new  material  from  out- 
side for  its  use  are  known  as  receptive  organs.  There  are 
two  chief  sets  of  these — one  to  receive  oxidizable  things,  and 
the  other  to  receive  oxygen.  The  first  set  is  represented  by 
the  alimentary  canal,  consisting  of  mouth,  gullet*  stomach, 
and  intestines.  It  takes  in  food  and  drink.  The  second  set 
consists  of  the  lungs,  with  the  air  passages  leading  to  them. 
Their  business,  as  receptive  organs,  is  to  absorb  oxygen. 

The  organs  whose  duty  it  is  to  get  rid  of  waste  materials 
formed  in  the  body  are  called  excretory  organs.  The  three 
most  important  excretory  organs  are  the  lungs,  the  kidneys, 
and  the  skin.  The  lungs  give  out  carbon  dioxide  gas  and 
water ;  the  kidneys  get  rid  of  urea  and  water ;  and  the  skin, 
of  water,  common  salt  and  a  minute  quantity  of  urea. 

The  Intermediate  Steps  between  Reception  and  Excre- 
tion.— Between  the  taking  of  oxidizable  substances  into  our 
mouths  and  oxygen  into  our  lungs,  and  the  return  of  oxidized 
matters  from  our  bodies  to  the  surrounding  world,  a  great 
many  intermediate  steps  take  place.  The  alimentary  canal 
(see  Fig.  i)  is  a  tube  which  runs  through  the  body  but  no- 
where opens  into  it.  So  long  as  food  lies  in  this  tube  it 
therefore  does  not  really  form  a  part  of  the  body,  and  is  of 
no  use  to  it ;  it  resembles  coals  in  the  tender  of  a  locomotive, 
waiting  to  be  transferred  to  the  furnace  In  our  bodies  the 
furnace  is  everywhere ;  wherever  there  is  living  tissue,  sub- 
stances are  burned  to  enable  it  to  work.  Hence  the  food  or 
fuel  must  be  brought  to  every  corner  of  our  frames. 

Digestion. — A  great  part  of  our  food  is  solid,  and  could 
not  of  itself  get  outside  of  the  alimentary  canal.  To  render 

*  The  technical  name  for  the  gullet  is  oesophagus. 


CIRCULATION,  RESPIRATION,  ETC.  #5 

it  available  it  must  be  dissolved  so  that  it  can  soak  through 
the  walls  of  the  stomach  and  intestines.  For  this  purpose 
we  find  a  set  of  digestive  organs  to  make  solvent  juices  and 
pour  them  upon  the  food  which  we  swallow,  and  so  get  it 
into  a  liquid  state  in  which  it  can  be  absorbed. 

Circulation. — If  the  solution  containing  our  digested  food 
simply  soaked  through  the  walls  of  the  alimentary  canal,  it 
could  not  reach  the  distant  parts,  as  the  brain  or  the  muscles 
of  the  limbs.  We  find,  therefore,  in  the  body  a  set  of  tubes 
containing  blood,  called  blood  vessels ;  the  blood  is  driven 
through  these  by  a  pump,  the  heart.  Much  of  the  dissolved 
food  passes  into  the  blood  vessels  of  the  alimentary  canal, 
and  from  them  is  carried  by  connecting  blood  vessels  to 
every  organ,  no  matter  how  remote.  As  the  blood  flows 
unceasingly,  round  and  round  in  its  vessels,  from  part  to 
part,  the  organs  concerned  in  moving  and  conveying  it  are 
called  circulatory  organs,  and  the  blood  flow  itself  is  known 
as  the  circulation. 

Absorbents. — Some  of  the  dissolved  food  is  taken  up  into 
another  set  of  tubes  in  the  walls  of  the  alimentary  canal; 
these  tubes  carry  it  afterwards  into  the  blood  vessels.  They 
are  called  the  absorbents,  or  lymphatics. 

Respiration. — The  blood  in  its  course  flows  through  the 
lungs.  It  is  necessary  not  merely  that  food  but  oxygen  also 
should  be  carried  to  every  part  of  the  body.  As  the  blood 
traverses  the  lungs  it  picks  up  oxygen  from  the  air  in  them ; 
this  air  is  then  replaced  by  taking  a  fresh  breath,  and  so  on. 
The  organs  thus  concerned  are  the  respiratory  organs,  and  the 
act  of  renewal  is  respiration. 

Assimilation. — As  each  organ  works  it  oxidizes  ;  some  of 
its  substance  is  broken  down  by  combination  with  oxygen 
brought  to  it  by  the  blood,  and  is  thus  converted  into  burnt 


S6  THE  HUMAN  BODY. 

waste  matter.  The  blood,  as  we  have  seen,  brings,  however, 
not  merely  oxygen  but  also  food  matters  in  solution.  These 
ooze  through  the  walls  of  the  blood  vessels,  and  are  taken  up 
by  the  living  tissues  and  built  into  new  tissues  like  them- 
selves, to  replace  the  part  which  has  been  used  up  and  de- 
stroyed. This  building  and  repair  of  tissues  and  organs  from 
the  dissolved  food  obtained  from  the  blood  is  known  as  as- 
similation — in  plain  English,  "a  making  alike."  Each  liv- 
ing tissue  takes  from  the  blood  foods  which  are  not  like 
itself,  and  builds  them  up  into  a  form  of  matter  like  its  own. 
The  converse  process,  which  accompanies  all  vital  action,  the 
breaking  down  into  wastes  of  a  living  tissue  when  it  works,  is 
called  dissimilation,  or  "a  making  unlike." 

The  Relation  of  the  Circulatory  Organs  and  the  Ab- 
sorbents to  Excretion. — It  is  essential  to  the  body  that  its 
wastes  be  carried  off.  Here  again  the  blood  vessels  and  ab- 
sorbents, or  lymphatics,  come  into  play.  Lymphatics  are 
found  not  only  in  the  walls  of  the  alimentary  canal,  but  all 
over  the  body.  The  wastes  of  each  working  tissue  are 
passed  out  into  them,  and  by  them  carried  into  the  blood 
vessels ;  these  in  turn  carry  the  wastes  to  the  lungs,  kidneys, 
and  skin  which  get  rid  of  them.  The  blood  is  thus  as  im- 
portant for  removing  the  waste  matters  of  an  organ  as  for 
supplying  it  with  food  and  oxygen. 

Nutrition. — From  what  has  been  said  above,  it  is  clear 
that  the  nourishment  of  the  body  is  a  very  complicated  pro- 
cess. It  implies — (i)  the  reception  of  food  from  outside; 
(2)  the  digestion  of  food;  (3)  the  absorption  of  digested 
food ;  (4)  the  absorption  of  oxygen  in  the  lungs,  and  its  con- 
veyance by  the  blood  to  every  organ  ;  (5)  the  conveyance  of 
absorbed  food  and  oxygen  to  all  parts  by  the  blood ;  (6)  as- 
similation or  the  building  up  of  new  tissue  from  materials 


NUTRITION.  87 

brought  by  the  blood;  (7)  disassimilation,  or  the  breaking 
down  of  working  tissues  by  combination  with  oxygen ;  (8) 
the  taking  up  of  wastes  from  the  different  organs  ;  and  (9)  the 
conveyance  of  these  wastes  by  the  blood  to  excretory  organs 
which  pass  them  out  of  the  body. 

In  subsequent  chapters  we  shall  have  to  consider  in  more 
detail  Digestion,  Circulation,  Absorption,  Respiration,  and 
Excretion.  The  sum  total  of  the  actions  of  all  the  organs 
concerned  in  the  nourishment  of  the  body  is  known  as  the 
function  of  nutrition.  As  will  be  explained  later,  some  of  the 
food  fulfils  other  purposes  than  the  formation  of  energy  yield- 
ing material. 


CHAPTER  X. 

FOODS. 

Foods  as  Tissue  Formers. — In  the  last  chapter  we  have 
considered  foods  merely  as  sources  of  energy,  but  they  are 
also  required  to  build  up  the  substance  of  the  body.  From 
birth  to  manhood  we  increase  in  bulk  and  weight  not  merely 
by  accumulating  water  and  such  substances,  but  by  forming 
more  bone,  more  muscle,  more  brain,  and  so  on,  from  the 
things  which  we  eat.  Even  after  full  growth,  when  the  body 
ceases  to  gain  weight,  there  are  probably  some  constructive 
processes  going  on  as  the  tissues  are  broken  down  and  recon- 
structed. 

Foods  are  therefore  needed  not  only  to  supply  the  body 
with  work-power  by  their  oxidation,  but  to  supply  material 
from  which  tissue  can  be  reconstructed. 

What  Foods  must  Contain. — Most  foods  serve  both  for 
energy  supply  *  and  tissue  formation  ;  they  are  probably  built 
up  by  the  living  cells  into  new  forms  before  they  are  oxidized 

*  Whether  any  food  is  ever  oxidized  in  the  body  before  being  built  up 
into  a  tissue,  as  coal  is  burnt  in  an  engine  without  ever  forming  part  of 
the  engine,  must  still  be  regarded  as  an  open  question  in  physiology. 
The  old  doctrine  that  some  foods,  as  starch  and  sugar,  were  useful  only 
to  set  free  heat,  and  others,  as  albumen  and  flesh,  alone  built  tissue,  must 
be  given  up.  It  seems  certain  that  under  some  conditions  sugar  and 
starch  may  be  used  in  building  tissue,  though  they  cannot  do  it  alone; 
but  whether  they  are  under  any  circumstances  ever  burnt  before  making 
part  of  a  tissue  is  not  certain.  On  the  other  hand,  there  is  reason  to 
suspect  that  albuminous  substances  may  be  oxidized  in  the  body  without 
ever  forming  part  of  a  living  cell. 

88 


THE  IMPORTANCE   OF  PROTEID  FOODS.  89 

to  set  the  energy  free.  The  living  tissues  when  analyzed  are 
found  to  consist  mainly  of  carbon,  hydrogen,  nitrogen,  and 
oxygen,  and  we  might  at  first  suppose  that  these  chemical  ele- 
ments in  their  uncombined  form  would  serve  to  nourish  us. 
Experience,  however,  teaches  that  this  is  not  the  case.  Four 
fifths  of  the  air  is  nitrogen,  but  we  cannot  feed  on  it ;  hydro- 
gen gas  is  of  no  use  as  a  food  ;  and  a  lump  of  charcoal  (car- 
bon) might  fill  the  stomach,  but  would  not  keep  a  man  from 
starving.  Oxygen  can  be  utilized  when  taken  by  the  lungs 
from  the  air ;  but  all  other  elements  to  be  of  use  as  food  must 
be  taken,  not  in  their  separate  state,  but  in  the  form  of  com- 
plex compounds,  in  which  they  are  chemically  combined  with 
other  things ;  as,  for  example,  in  starch,  sugar,  fat,  oil,  and 
albuminous  substances. 

'  The  Special  Importance  of  Albuminous  or  Proteid 
Foods. — All  the  active  tissues  of  the  body  are  found  to  yield 
on  chemical  analysis  large  quantities  of  proteids.  (See  p.  15.) 
So  far  as  we  know  at  present  the  human  body  (like  that  of 
most  animals)  is  unable  to  make  proteids  out  of  other  things. 
Given  one  variety  of  them  it  can  turn  it  into  other  varieties, 
but  it  cannot  make  proteids  from  things  which  are  not  pro- 
teids. Hence  these  albuminous  or  proteid  substances  are  an 
essential  article  of  diet. 

The  Limited  Constructive  Power  of  the  Animal  Body. — • 
From  what  has  been  said  above,  it  is  clear  that  our  bodies 
are,  on  the  whole,  destructive  rather  than  constructive  in  re- 
lation to  the  outer  world.  They  require  for  their  nutrition 
very  complex  chemical  compounds  (starch,  sugar,  fat,  pro- 
teids),* build  these  up  into  living  tissues,  or  oxidizable  forms, 

*  Starch C6H10O5 

Sugar C6H,.2O6 

Fat  (variable) C51H104O9 

Proteid  (variable) C72Hn a N, BO22S 


90  THE  HUMAN  BODY. 

then  oxidize  them  and  return  the  carbon,  hydrogen,  and 
nitrogen  to  the  outer  world  in  much  simpler  chemical  com- 
pounds (carbon  dioxide,  water,  and  urea).  None  of  these 
latter  substances  is  capable  of  nourishing  an  animal ;  it  cannot 
use  them  to  build  up  its  tissues  or  set  energy  free. 

How  Plants  Supply  Food  for  Animals,  and  Animals 
Food  for  Plants. — Since  animals  cannot  utilize  the  simple  sub- 
stances furnished  by  nature  as  food,  but  must  consume  com- 
plex substances,  as  proteids,  fat,  and  sugar,  the  question  nat- 
urally suggests  itself,  How  is  it  that  the  supply  of  these  is 
kept  up  ?  For  example,  the  supply  of  proteids,  which  can- 
not be  made  artificially  by  any  process  known  to  us.  The 
answer  is,  that  animals  live  on  the  things  which  plants  make, 
and  plants  live  on  the  carbon  dioxide,  water,  and  ammonia 
(urea)  which  animals  excrete. 

As  regards  our  own  bodies  the  question  might,  indeed,  be 
apparently  answered  by  saying  that  we  get  our  proteids  from 
the  flesh  of  the  other  animals  which  we  eat.  But  then  we 
have  to  account  for  the  possession  of  proteids  by  those  ani- 
mals, since  they  cannot  make  them  from  urea,  carbon  di- 
oxide, and  water  any  more  than  we  can.  The  animals  whose 
flesh  is  used  by  us  as  food  get  their  proteids  from  plants, 
which  are  the  great  proteid  formers  of  the  world.  The  most 
carnivorous  animal  really  depends  for  its  essential  food  upon 
the  vegetable  kingdom ;  the  fox  that  devours  a  hare  lives 
on  the  proteids  of  the  plants  which  the  hare  had  previously 
eaten  and  built  into  his  own  tissues. 

Non-oxidizable  Foods. — Besides  our  oxidizable  foods  a 
large  number  of  necessary  food  materials  are  not  oxidizable, 
or  at  least  are  not  oxidized  in  the  body.  Typical  instances 
are  afforded  by  water  and  common  salt.  The  use  of  these  is 
in  great  part  physical :  the  water,  for  instance,  dissolves  ma- 


GENERAL   CONSIDERATIONS  OF  FOODS.  91 

terials  in  the  alimentary  canal,  and  carries  the  solutions 
through  its  walls  into  the  blood  and  lymph  vessels,  so  that 
they  can  be  conveyed  from  place  to  place ;  and  it  permits 
interchanges  by  enabling  the  things  it  has  dissolved  to  soak 
through  the  walls  of  the  vessels.  The  salines  also  influence 
the  solubility  and  chemical  interchanges  of  other  things 
present  with  them.  Fibrinogen,  one  of  the  proteids  which  is 
carried  in  the  blood  all  over  the  body  to  supply  albuminous 
material  to  the  tissues,  is,  for  example,  insoluble  in  pure 
water,  but  dissolves  readily  if  a  small  quantity  of  common 
salt  is  present.  Beside  such  uses,  the  non-oxidizable  foods 
have  probably  other  functions  :  for  example,  the  lime  salts 
give  their  hardness  to  the  bones  and  teeth.  The  body  is  a 
self-building  and  self-repairing  machine,  and  the  material  for 
this  building  and  repair,  as  well  as  the  fuel  or  oxidizable 
foods  which  yield  the  energy  the  machine  expends,  must  be 
supplied  in  the  food.  While  experience  shows  us  that  even 
for  machinery  construction  oxidizable  matters  are  largely 
needed,  it  is  nevertheless  a  gain  to  replace  such  substances 
by  non-oxidizable  material  when  possible ;  just  as,  if  prac- 
ticable, it  would  be  advantageous  to  construct  an  engine  out 
of  a  substance  which  would  not  rust,  although  other  condi- 
tions determine  the  selection  of  iron  for  building  the  greater 
part  of  it. 

General  onsiderations. — Foods  to  replace  matters  which 
have  been  oxidized  must  be  themselves  oxidizable ;  they 
are  force  generators,  but  may  be  and  generally  are  also 
tissue  formers.  They  are  nearly  always  complex  organic  sub- 
stances derived  from  other  animals  or  from  plants.  Foods 
to  replace  matters  not  oxidized  in  the  body,  as  water  and 
salt,  are  force  regulators,  and  are  for  the  most  part  fairly 
simple  inorganic  compounds.  Among  the  force  regulators 


92  THE  HUMAN  BODY. 

we  must,  however,  include  certain  foods,  which,  although 
oxidized  in  the  body  and  serving  as  sources  of  energy,  yet 
produce  effects  greatly  out  of  proportion  to  the  amount  of 
energy  which  they  thus  set  free.  Their  influence  as  stimu- 
lants in  exciting  certain  tissues  to  activity,  or  as  agents  check- 
ing the  activity  of  parts,  is  more  marked  than  their  direct 
action  as  force  generators,  and  they  may  be  classed  as  acces- 
sory foods.  As  examples  we  may  take  condiments:  mustard 
and  pepper  are  not  of  much  use  as  sources  of  energy, 
although  they  no  doubt  yield  some  when  oxidized  ;  we  take 
them  for  their  stimulating  effect  on  the  mouth  and  other 
parts  of  the  alimentary  canal,  by  which  they  promote  a 
greater  flow  of  the  digestive  secretions  or  an  increased  appe- 
tite for  food.  Thein,  again,  the  active  principle  of  tea  and 
coffee,  is  taken  for  its  stimulating  effect  on  the  nervous  sys- 
tem rather  than  for  the  amount  of  energy  which  is  yielded 
by  its  own  oxidation. 

To  the  above  consideration  of  foods  should  be  added  the 
condition  that  neither  the  substance  itself  nor  any  of  the 
products  of  its  chemical  transformation  in  the  body  shall  be 
injurious  to  the  structure  or  action  of  any  organ  ;  otherwise  it 
is  a  poison,  not  a  food* 

Alimentary  Principles. — The  substances  which  we  call 
foods  are  usually  mixtures  of  several  foodstuffs  with  sub- 
stances which  are  not  foods  at  all.  Bread,  for  example,  con- 
tains water,  salts,  gluten  (a  proteid),  some  fats,  much  starch, 
and  a  little  sugar;  all  these  are  true  foodstuffs,  but  mixed 
with  them  is  a  quantity  of  cellulose  (the  chief  chemical  con- 
stituent of  the  walls  which  surround  vegetable  cells),  which 

*  This,  of  course,  is  true  only  when  the  substances  are  taken  in  the 
ordinary  moderate  or  physiological  amounts.  Many  substances  become 
harmful  or  poisonous  if  taken  in  excess,  e.g.  oxygen,  salt,  meat,  etc. 


PROTEID  ALIMENTARY  PRINCIPLES.  93 

is  not  a  food,  since  it  is  incapable  of  digestion  and  absorption 
from  the  alimentary  canal.  Chemical  examination  of  all  the 
common  articles  of  diet  shows  that  the  actual  number  of  im- 
portant foodstuffs  is  small ;  they  are  repeated  in  various  pro- 
portions in  the  different  foods  we  eat,  mixed  with  small 
quantities  of  different  flavoring  substances,  and  so  give  us  a 
pleasing  variety  in  our  -meals ;  but  the  essential  substances 
are  much  the  same  in  the  fare  of  the  artisan  and  in  the  "  deli- 
cacies of  the  season."  The  chief  foodstuffs,  which  are  found 
repeated  in  many  different  foods,  are  known  as  "alimentary 
principles, ' '  and  the  nutritive  value  of  any  article  of  diet  de- 
pends on  the  amount  of  these  foodstuffs  present,  far  more 
than  on  the  various  agreeable  flavoring  matters  which  cause 
certain  things  to  be  sought  after  and  to  have  a  high 
market  value.  Alimentary  principles  may  be  conveniently 
classified  into '  proteids,  fats,  carbohydrates,  and  inorganic 
bodies. 

Proteid  Alimentary  Principles. — Of  the  nitrogenous  food- 
stuffs the  most  important  are  proteids  :  they  form  an  essential 
part  of  all  diets,  and  are  obtained  both  from  animals  and 
plants.  The  most  common  and  abundant  are  myosin  and 
syntonin,  found  in  the  lean  of  all  meats,  egg  albumin,  casein 
of  milk  and  cheese,  gluten  and  vegetable  casein  from  various 
plants. 

Beside  these  proteid  substances,  all  of  which  are  apparently 
able  to  act  as  tissue  builders,  there  is  a  class  of  nitrogenous 
substances  which  do  not  possess  this  power  though  they  are 
oxidized  in  the  body  to  yield  energy.  This  class  is  repre- 
sented by  gelatin,  derived  from  connective  tissue  and  bones, 
and  by  chondrin,  from  cartilage.  As  force  producers  they 
have  considerable  value,  but  are  not  nearly  as  important  food 
for  invalids  as  was  at  one  time  supposed. 


94  THE  HUM4N  BODY. 

Necessity  of  Proteid  Food.  —  Experiments  have  shown  that 
the  excretion  of  nitrogen  (chiefly  as  urea)  in  a  well-fed 
animal  is  equal  to  the  amount  of  nitrogen  taken  in  with  the 
food.*  This  balance  of  income  and  expenditure  is  called 
nitrogenous  equilibrium.  If  the  nitrogen  of  the  food  is  reduced 
below  a  certain  amount,  more  nitrogen  is  excreted  than  is 
replaced  by  the  food.  This  excess  of  expenditure  comes  from 
the  fleshy  tissues  of  the  animal,  which  are  thus  wasted  away. 
All  animals  thus  become  flesh-eating  (carnivorous)  when 
starving. 

Fats  and  Oils.  —  The  most  important  of  these  are  stearin, 
palmatin,  margarin,  and  olein,  which  exist  in  various  pro- 
portions in  animal  fats  and  vegetable  oils,  and  butter,  which 
contains  a  peculiar  fat  known  as  butyrin.  All  fats  are  com- 
pounds of  glycerin  with  fatty  acids,  and,  speaking  generally, 
are  useful  as  food  if  fusible  at  the  temperature  of  the  body. 
The  stearin  of  beef  and  mutton  fats  is  not  by  itself  fusible  at 
the  body  temperature,  but  as  eaten  it  is  mixed  with  so  much 
olein  as  to  be  melted  in  the  alimentary  canal. 

Artificial  butters,  such  as  margarin,  oleomargarin,  butter- 
ine,  and  cocoa  butter,  are  made  of  the  more  easily  melted 
animal  or  vegetable  fats  flavored  to  resemble  butter  by  being 
churned  in  butter  milk.  They  are  easily  digested  and  pos- 
sess practically  the  same  nutritive  value  as  butter. 

Fats  and  oils  are  rich  in  carbon  and  hydrogen,  but  contain 
little  oxygen.  Hence  their  oxidation  liberates  much  energy. 

Fat.  Oxygen.        Carbon  dioxide.          Water. 

CH980 


Carbohydrates.  —  These  are  mainly  of  vegetable   origin. 
The  most  important  are  starch  (found  in  nearly  all  vegetable 

*  While  an  animal  is  growing,  the  excretion  of  nitrogen  is  slightly  less 
than  the  income  owing  to  its  storage  in  the  growing  flesh. 


INORGANIC  FOODS.  95 

foods),  dextrin,  gums,  grape  sugar  (found  in  most  fruits),  and 
cane  sugar.  Sugar  of  milk  and  glycogen  (animal  starch  from 
the  liver)  are  alimentary  principles  of  this  group  derived 
from  animals.  All  carbohydrates,  like  the  fats,  consist  of 
carbon,  hydrogen,  and  oxygen,  but  the  percentage  of  oxygen 
in  them  is  much  higher  than  in  fats.  In  fact  oxygen  is 
present  in  just  the  right  proportion  to  satisfy  all  the  hydro- 
gen ;  hence  only  carbon  remains  to  be  oxidized.  They 
have  therefore  less  power  of  combining  with  additional  oxy- 
gen than  fats  and  so  are  not  capable  of  yielding  as  much 
energy  to  the  body. 

Sugar.  Oxygen.     Carbon  dioxide.      Water. 

=    6C°        6H0- 


Fuel  Values  of  Food  Principles.  —  The  heat  produced  by 
the  combustion  of  weighed  quantities  of  food  materials  has 
been  determined  by  numerous  experimenters,  and  the  average 
of  the  results  is  expressed  in  the  following  table  : 

Calories.      Foot-tons. 

I  gram  of  proteid  (dry)  ........    4.  i  6.3 

i      "      "fats  ................    9.3         14.2 

i      "      "carbohydrates  (dry)..    4.1  6.3 

Experiments  have  further  shown  that  the  energy  produced 
in  the  body  (heat,  muscular  work,  etc.  )  by  the  oxidation  of 
the  food  substances  is  practically  equivalent  to  that  obtained 
by  combustion.* 

*  The  heat  units  used  by  physiologists  represent  the  amount  of  heat 
necessary  to  raise  the  respective  amounts  of  water  one  degree  Centigrade. 
I.  kilo        water  i°  C.  =  Calorie  =  i.o         pound  water  4°  F. 

I.  gram  "      1°  C.  =  calorie  =  o.ooi.          "          "      4°  F. 

o.ooi  gram  "  i°  C.  r=  micro-calorie  =  o.oooooi  "  "  4°  F. 
One  Calorie  is  equivalent  in  mechanical  energy  to  1.53  foot-  tons. 
One  calorie  "  <'  ««  «  «  "  0.00153  " 


96  THE  HUMAN  BODY. 

Inorganic  Foods. — The  most  important  of  these  are  water, 
common  salt,  and  the  chlorides,  the  phosphates  and  the  sul- 
phates of  potassium,  magnesium,  and  calcium.  A  sufficient 
quantity  of  most  of  these  substances,  or  of  the  material  for 
their  formation,  exists  in  all  ordinary  articles  of  diet,  so  that 
we  do  not  take  them  in  a  separate  form.  Water  and  table 
salt  form  exceptions  to  the  rule  that  inorganic  bodies  are 
eaten  imperceptibly  along  with  other  things,  since  the  body 
requires  more  of  each  daily  than  is  usually  supplied  in  that 
way.  It  has  been  maintained  that  salt  as  a  separate  article  of 
diet  is  an  unnecessary  luxury,  and  there  seems  to  be  some  evi- 
dence that  certain  savage  tribes  live  without  more  than  they 
get  in  the  meat  and  vegetables  which  they  eat.  Such  tribes 
are,  however,  said  to  suffer  from  intestinal  parasites;  and 
there  is  no  doubt  that  to  many  animals  as  well  as  most  men 
the  absence  of  salt  from  their  diet  is  a  terrible  deprivation. 
Buffaloes  and  other  creatures  are  well  known  to  travel  miles 
to  reach  ' '  saltlicks  " ;  of  two  sets  of  oxen,  one  allowed  free 
access  to  salt,  and  the  other  given  none  save  what  existed  in 
its  ordinary  food,  it  was  found  after  a  few  weeks  that  those 
given  salt  were  in  much  better  condition.  In  man  the  desire 
for  salt  is  so  great  that  in  regions  where  it  is  scarce  it  is  used 
as  money.  In  some  parts  of  Africa  a  small  quantity  of  salt 
will  buy  a  slave,  and  to  say  that  a  man  commonly  uses  salt  at 
his  meals  is  equivalent  to  stating  that  he  is  a  millionaire.  In 
British  India,  where  the  poorer  natives  regard  so  few  things 
as  necessaries  of  life  that  it  is  hard  to  levy  any  excise  tax,  a 
large  part  of  the  revenue  is  derived  from  a  tax  on  salt,  which 
even  the  poorest  will  buy.  In  the  Austrian  Empire  it  has 
been  found  that  youths  who  have  fled  to  the  mountains  and 
there  led  a  wild  life  to  avoid  military  conscription,  will  come 


NUTRITIVE  VALUE  OP  DIFFERENT  FOODS.  97 

down  to  the  villages  to  purchase  salt,  at  the  risk  of  liberty 
and  even  of  life. 

The  Nutritive  Value  of  Different  Poods. — All  meats, 
whether  derived  from  beast,  bird,  or  fish,  are  highly  valuable 
foods.  They  contain  abundant  albumen,  more  or  less  fat, 
and  when  cooked,  their  connective  tissue  is  in  great  part  made 
soluble  by  being  turned  into  gelatine.  Pork  is  the  least  easily 
digested  form  of  fresh  meat,  since  it  contains  a  larger  per- 
centage of  fat  than  most.  This  fat,  which,  by  its  oxidation 
liberates  much  heat,  makes  it  a  good  food  in  cold  weather  for 
persons  with  a  good  digestion.  Pigs  are,  however,  especially 
liable  to  a  dangerous  parasite,  called  trichina,  which  lives  in 
their  muscles,  and  may  be  transferred  to  man  if  the  pork  is 
not  thoroughly  cooked.  Salted  meats  of  all  kinds  are  less 
digestible  and  less  nutritious  than  fresh.  Milk  contains  an 
albuminous  substance  (casein),  also  fats  (butter),  and  sugar, 
known  as  sugar  of  milk,  in  addition  to  useful  mineral  salts. 
It  will  support  life  longer  than  any  other  single  food.  Cheese 
consists  essentially  of  the  casein  of  milk,  and  is  a  very  nutri- 
tive albuminous  food.  Eggs  contain  albumens  and  fats  of 
high  nutritive  value,  but  they  are  not  easily  digested  when 
cooked  too  long.  Wheat  contains  more  than  a  tenth  of  its 
weight  of  proteids,  more  than  half  its  weight  of  starch,  some 
sugar,  and  a  little  fat.  The  proteid  of  wheat  flour  is  mainly 
gluten,  which  when  moistened  with  water  forms  a  tenacious 
mass,  and  gives  to  wheat  bread  its  superiority.  When  the 
dough  is  made,  yeast  is  added  to  it  and  causes  fermentation 
by  which  some  of  the  starch  is  changed  into  sugar,  then 
into  alcohol  and  carbon  dioxide.  If  the  fermentation  is 
allowed  to  go  too  far,  the  alcohol  is  changed  into  acetic 
and  other  acids,  and  sour  bread  results.  The  carbon  dioxide 


9     •  THE  HUMAN  BODY. 

imprisoned  in  the  tenacious  -dough  and  expanded  by  heat 
during  baking,  forms  cavities  in  it,  and  causes  the  dough  to 
"rise"  and  make  "light  bread,"  which  is  not  only  pleas- 
anter  to  eat  but  more  easily  digested  than  heavy.  Some 
grains  conjtain  a  larger  percentage  of  starch,  but  less  gluten, 
than  wheat ;  when  bread  is  made  from  them  the  carbon 
dioxide  gas  escapes  so  readily  from  the  less  tenacious  dough 
that  it  does  not  expand  the  mass  properly.  Corn  contains 
less  proteid,  more  starch,  and  more  fat  than  wheat  and  is 
very  nutritious.  Rice  is  poor  in  proteids,  but  very  rich  in 
starch.  Peas  and  beans  are  rich  in  proteids  and  contain  about 
half  their  weight  of  starch.  Potatoes  contain  a  great  deal  of 
water  and  only  about  two  parts  of  proteids  and  twenty  of 
starch  in  a  hundred  parts  by  weight,  but  are  rich  in  useful 
salts.  Other  fresh  vegetables,  as  carrots,  turnips,  and  cabbages, 
as  well  as  fruits,  are  valuable  mainly  for  the  salts  they  con- 
tain ;  their  weight  is  chiefly  due  to  water,  and  they  contain 
but  little  starch,  proteids,  or  fats.  Some  kind  of  fresh  vege- 
table is,  however,  a  necessary  article  of  diet,  as  shown  by 
the  scurvy  *  which  used  to  prevail  among  sailors  before  fresh 
vegetables  or  lime-juice  were  supplied  to  them. 

Alcohol  as  a  Food. — Evidence  goes  to  show  that  alcohol 
in  moderate  doses  is  oxidized  in  the  body  and  yields  energy, 
but  cannot  build  up  or  restore  exhausted  tissue.  In  certain 
diseases  the  fact  that  it  requires  no  digestion  and  is  rapidly 
absorbed  gives  it  considerable  value.  The  amount  of  alcohol 
which  can  be  taken  for  food,  however,  is  so  slight  because  of 
its  marked  stimulating  effect  that  under  normal  conditions  it 
is  practically  valueless  for  food  purposes.  Its  frequent  use 

*  Scurvy  is  characterized  by  swelling  and  bleeding  of  the  gums, 
loosening  of  the  teeth,  and  great  weakness  ending  in  death.  It  was 
especially  frequent  among  whalers. 


TEA  AND  COFFEE— COOKING.  99 

may  undoubtedly  lead  to  a  serious  diminution  of  vitality, 
lessened  resistance  to  disease,  diminished  endurance  of  fatigue, 
heat,  and  cold,  and  to  pathological  conditions  of  the  vital 
organs,  such  as  an  overgrowth  of  connective  tissue  and  fat. 
The  consumption  of  alcohol  has  so  frequently  led  to  wasted 
opportunities,  suffering,  and  even  crime  that  it  is  the  part  of 
wisdom  to  avoid  its  use. . 

Tea  and  Coffee  are  to  be  regarded  as  stimulants  rather  than 
foods.  The  amount  of  nourishment  in  a  cup  of  either  is  but 
little.  Both  have,  however,  some  influence  in  removing  the 
sense  of  fatigue,  and  when  occasionally  taken  in  moderate 
doses  leave  as  a  rule  no  injurious  after-effects.  For  relieving 
fatigue,  tea  and  coffee  are  superior  to  alcohol,  but  neither 
should  be  used  as  a  substitute  for  rest  and  sleep ;  in  fact  it 
may  be  questioned  whether  the  habitual  use  of  either  is 
advisable.  Sportsmen  out  for  a  long  day's  shooting  find  cold 
tea  superior  to  spirits ;  military  commanders  find  a  ration  of 
coffee  far  better  than  one  of  whiskey  for  fatigued  troops,  and 
all  arctic  explorers  have  come  to  a  similar  conclusion. 

Cooking. — When  meat  is  cooked  most  of  its  connective 
tissue  is  turned  into  gelatin,  and  the  whole  mass  becomes 
softer  and  more  readily  broken  up  by  the  teeth.  In  boiling 
meat  it  is  a  good  plan  to  put  it  first  into  boiling  water  in 
order  to  coagulate  the  albumen  at  the  surface  and  thus  form 
a  dense  coat  which  keeps  flavoring  matters  and  salts  from 
passing  into  the  water.  After  the  first  few  minutes  the  cook- 
ing should  be  continued  at  a  lower  temperature ;  meat  boiled 
too  fast  is  hard,  tough,  and  stringy.  In  roasting  or  baking 
meat,  it  is  also  advisable  to  put  it  close  to  the  fire  or  in  a 
hot  oven  for  a  short  time,  and  then  to  complete  the  cooking 
more  slowly. 

The  cooking  of  vegetable  foods  is  of  considerable  impor- 


loo  THE  HUMAN  BODY. 

'..ance.  Starch  is  the  chief  nutrient  matter  in  most  of  them, 
and  raw  starch  is  much  less  easily  digested  than  cooked 
since  it  is  enclosed  in  a  thick  cell  wall  of  indigestible  cellulose 
which  is  broken  down  by  cooking.  When  starch  is  heated 
it  is  turned  into  a  substance  known  as  soluble  starch,  which  is 
easily  dissolved  by  the  digestive  liquids ;  there  is  therefore  a 
scientific  foundation  for  the  common  belief  that  the  crust  of 


FlG.  44. — Cells  of  a  raw  potato,  with  starch  grains  in  natural  condition. 

a  loaf  is  more  digestible  than  the  inside,  and  toast  than  fresh 
bread. 

The  Oxidizable  Matters  Required  Daily  by  the  Body.— 

The  amount  of  food  required  daily  depends  upon  the  quantity 
of  material  used  up  by  the  body  in  each  twenty-four  hours ; 
this  varies  both  in  kind  and  amount  with  the  work  done 
and  the  organs  most  used.  In  children  a  certain  excess  is 
required  to  furnish  material  for  growth.  It  is  impossible  to 
state  accurately  beforehand  just  what  any  individual  will 
require,  but  a  general  idea  may  be  arrived  at  by  taking 
the  average  daily  losses,  by  excretion,  as  determined  by  many 
experiments  made  on  different  persons.  Such  experiments 
show  that  a  man  of  average  size  and  doing  ordinary  work 
needs  rather  more  than  274  grams  (9!  ounces)  of  carbon  to 


ADVANTAGES  Of  A  MIXED  DIET,  101 

replace  his  loss  of  that  element,  and  about  20  grams  of  nitro- 
gen (T7¥  of  an  ounce).  Some  hydrogen  is  also  required, 
as  the  body  daily  excretes  more  water  than  it  receives 
through  food  and  drink  ;  this  extra  amount  implies  a  loss  of 
hydrogen,  which  has  combined  with  oxygen  in  the  body  to 
form  water. 

The  Advantages  of  a  Mixed  Diet. — Since  proteid  foods 
contain  carbon,  nitrogen,  and  hydrogen,  life  may  be  main- 
tained on  them  if  the  necessary  salts,  water,  and  oxygen  be 
also  supplied;  but  such  a  diet  would  not  be  economical. 
Ordinary  proteids  contain  in  100  parts  about  52  of  carbon 
and  15  of  nitrogen,  so  a  man  fed  on  them  alone  would 
get  about  3!  parts  of  carbon  for  every  i  of  nitrogen.  His 
daily  losses  are  not  in  this  ratio,  but  about  15  parts  of  carbon 
to  i  of  nitrogen  :  therefore  to  get  enough  carbon  from  pro- 
teids far  more  than  the  necessary  amount  of  nitrogen  must  be 
taken.  Of  dry  proteids  527  grams  (i  pound  2-J-  ounces) 
would  yield  the  necessary  carbon,  but  would  contain  79 
grams  (2!  ounces)  of  nitrogen,  or  four  times  more  than 
is  necessary  to  cover  the  daily  losses  of  that  element  from  the 
body.  Fed  on  a  purely  proteid  diet  a  man  would,  therefore, 
have  to  digest  a  vast  quantity  to  get  enough  carbon,  and  in 
eating  and  absorbing  it,  and  in  getting  rid  of  the  excess 
nitrogen,  a  great  deal  of  unnecessary  labor  would  be  thrust 
upon  the  digestive  and  excretory  organs.  Were  a  man  to 
live  on  bread  alone,  he  would  also  force  much  unnecessary 
work  on  his  organs.  Bread  contains  little  nitrogen  in  pro- 
portion to  its  carbon,  and  to  get  enough  nitrogen  far  more 
carbon  than  could  be  utilized  would  have  to  be  eaten  and 
digested  daily. 

The  human  race  has  discovered  this  fact :   men  use,  where 
they  have  a  choice,  richly  proteid  substances  to  supply  the 


t62  THE  HUMAN  BODY. 

nitrogen  needed,  but  derive  the  carbon  mainly  from  non- 
nitrogenous  foods  of  the  fatty  carbohydrate  kinds,  and  so 
avoid  excess  of  either  nitrogen  or  carbon.  For  instance,  lean 
beef  contains  about  25  per  cent  of  dry  proteid,  and  this  in 
turn  contains  15  per  cent  of  nitrogen.  Consequently  542 
grams  (i  pound  3  ounces)  of  lean  meat  would  supply  the 
nitrogen  needed  to  compensate  for  a  day's  losses.  But  the 
proteid  contains  52  per  cent  of  carbon,  so  the  amount  of 
carbon  in  the  above  weight  of  fatless  meat  would  be  69  grams 
(or  nearly  2^-  ounces),  leaving  205  grams  (or  rather  more 
than  7  ounces)  to  be  got  either  from  fats  or  carbohydrates. 
The  necessary  amount  is  contained  in  256  grams  (or  about  9 
ounces)  of  ordinary  fats,  or  in  460  grams  (a  little  over  a 
pound)  of  starch  ;  hence  either  of  these  with  the  above  quan- 
tity of  lean  meat  would  form  a  far  better  diet  both  for  the 
system  and  the  purse  than  meat  alone. 

As  already  pointed  out,  nearly  all  common  foods  contain 
several  foodstuffs.  Good  butcher's  meat,  for  example,  con- 
tains nearly  half  its  dry  weight  of  fat,  and  bread  in  addition 
to  proteids  contains  starch,  fats,  and  sugar.  In  neither  of 
them,  however,  are  the  foodstuffs  mixed  in  the  physiologi- 
cally best  proportions,  and  the  custom  of  consuming  several 
of  them  at  each  meal,  or  different  ones  at  different  meals  dur- 
ing the  day,  is  not  only  agreeable  to  the  palate  but  in  a  high 
degree  advantageous  to  the  body.  The  strict  vegetarians  who 
do  not  eat  even  such  substances  as  eggs,  cheese,  and  milk, 
but  confine  themselves  to  a  purely  vegetable  diet,  which  is 
always  poor  in  proteids,  take  daily  far  more  carbon  than  they 
require,  and  are  to  be  congratulated  on  their  excellent  diges- 
tions which  are  able  to  stand  the  strain.  Those  so-called 
vegetarians  who  use  eggs,  cheese,  and  other  animal  substances 
can  of  course  get  on  very  well,  since  these  are  extremely  rich 


RELATION  OF  DIET  TO  WORK.  103 

in  proteids,  and  supply  all  the  nitrogen  needed,  without  the 
necessity  of  swallowing  the  vast  bulk  of  food  which  must  be 
eaten  in  order  to  get  it  directly  from  plants. 

Food  Materials. — The  above  facts  are  best  shown  in  the 
chemical  analyses  of  food  materials.  Detailed  diet  studies 
have  made  it  possible  to  construct  meals  based  on  the  actual 
nutritive  values  of  different  foods,  which  shall  give  an  ade- 
quate amount  of  nutriment  to  individuals  of  varying  pursuits. 

In  the  study  of  the  dietaries  it  has  been  found  that  the  es- 
sential points  to  be  observed  are  the  total  amount  of  nitroge- 
nous material  (proteid)  and  the  total  fuel  value  of  all  the 
elements.  It  has  been  found  that  the  fats  and  starches  are 
largely  interchangeable  in  the  ordinary  dietaries,  hence  their 
proportions  are  of  less  importance. 

Relation  of  Diet  to  Work. — It  must  be  remembered  that 
energy  is  given  off  in  the  form  of  heat,  and  is  used  up  in  the 
body  by  the  heart  (as  explained  later),  and  by  tissue  activity. 
The  external  work  accomplished  by  a  man  under  different 
conditions  is  shown  in  the  following  table,  together  with  the 
heat  equivalents  for  this  work.  The  amount  of  work  accom- 
plished is  most  readily  expressed  in  foot-tons.* 

ESTIMATES  OF  MECHANICAL  WORK   DONE   BY  A   MAN   IN  A  DAY. 

Foot-tons.  Kilogrammetres.            Calories  of  Heat. 

Light       work,  from  150  to  200  or     46,600  to    62,200     or     109  to  147 

Average      "         "      300  "  350  "      93,300  "  108,800     •'      219  "  258 

Hard           "          "      450  "  500  "    139,900  "  155,500     "      329  "  366 

Laborious  "         "      500  "  600  "    155,500  "  186,000     "      366  "  437 

Protein.  Fats.  $*£.          Fuel  Value. 

Standard  Diet,  Atwater     127  gms.      113  gms.     494  gins.     35OoCalories. 

*  Each  foot-ton  represents  the  effort  necessary  to  raise  the  equivalent 
of  one  ton  to  a  height  of  one  foot.  This  is  equivalent  to  raising  one 
pound  to  a  height  of  two  thousand  feet.  A  kilogrammetre  measures  the 
effort  necessary  to  raise  one  kilogram  (2^  Ibs.)  to  a  height  of  one  metre 
(3|  ft-)- 


IO4 


THE  HUMAN  BODY. 


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RELATION  OF  DIET   TO   WORK.  105 

In  comparing  these  figures  with  the  number  of  heat  units  in 
Atwater's  standard  diet  it  will  be  noticed  that  only  about 
one-tenth  of  the  energy  value  of  the  food  is  utilized  for  ex- 
ternal work  ;  the  remaining  nine-tenths  are  used  up  in  doing 
the  internal  work  of  the  body  and  in  making  good  the  heat 
losses.  It  has  been  estimated  that  in  muscular  work  only 
one-third  of  the  energy  of  the  food  fs  converted  into  mechan- 
ical work  by  the  muscle,  the  remaining  two-thirds  being  dis- 
sipated as  heat. 


CHAPTER  XI. 
THE  DIGESTIVE  ORGANS. 

General  Arrangement  of  the  Alimentary  Canal. — The 

alimentary  canal  is  a  tube  which  runs  through  the  body  from 
the  lips  to  the  posterior  end  of  the  trunk.  It  is  lined  by  a 
soft  reddish  mucous  membrane  (easily  seen  inside  the  mouth), 
which  is  but  a  redder  and  moister  sort  of  skin.  Outside  the 
mucous  membrane  are  connective  tissue  and  muscular  layers, 
which  strengthen  the  digestive  tube  and  push  the  swallowed 
food  along  it.  The  mucous  membrane  is  constructed  to  ab- 
sorb dissolved  nutritive  substances  ;  it  soaks  them  up  and 
passes  them  into  blood  or  lymph  vessels.  Imbedded  in  this 
mucous  membrane,  or  lying  outside  it,  are  hollow  organs 
called  glands  ;  these  glands  make  liquids  which  change  food 
substances  chemically  so  that  they  may  be  absorbed  by  the 
mucous  membrane.  The  whole  series  of  changes  which  any 
food  material  undergoes,  between  its  reception  by  the  mouth 
and  its  absorption  by  the  alimentary  mucous  membrane,  is 
spoken  of  as  its  digestion. 

Various  foodstuffs  undergo  different  kinds  of  changes  pre- 
liminary to  absorption,  and  so  we  speak  of  different  kinds  of 
digestions ;  as  that  of  starch,  of  fats,  of  albuminous  bodies, 
and  so  forth. 

Glands  are,  ordinarily,  hollow  organs  which  make  or  secrete 
peculiar  fluids  and  pour  them  out  on  some  free  surface  of  the 

106 


THE  KINDS   OF  GLANDS.  107 

body.  They  are  very  widely  distributed  ;  we  find,  for  exam- 
ple, digestive  glands  of  several  kinds  opening  into  the  di- 
gestive tube,  perspiratory  glands  opening  on  the  skin,  tear  or 
lachrymal  glands  pouring  out  their  secretion  on  the  eyeball. 
Different  glands  have  their  cavities  lined  by  different  kinds 
of  cells,  and  produce  different  secretions.  In  general  all 
glands  are  built  on  one  or  the  other  of  two  primary  structural 
plans,  known  as  the  tubular  and  the  racemose  (Fig.  45). 

The  Kinds  of  Glands. — All  portions  of  the  body  making 
and  pouring  forth  secretions  are  not  technically  called  glands. 
In  the  peritoneum,  which  forms  the  inside  lining  of  the  ab- 
dominal cavity  (p.  8),  we  find  simply  a  thin  membrane  (A, 
Fig.  45),  having  on  the  side  next  the  cavity  which  it  sur- 
rounds a  layer  of  cells  (a]  and  on  its  deeper  side  a  network 
of  very  fine  blood-vessels  (c)  supported  by  connective  tissue 
(</).  This  arrangement  is  also  found  in  the  pleurae,  the  pericar- 
dium, and  the  synovial  membranes,  but  is  not  the  most  com- 
mon form  of  secreting  tissue.  In  most  cases  the  area  of  the 
surfaces  necessary  to  secrete  the  amounts  of  the  various  fluids 
needed  would  be  too  great  to  be  packed  conveniently  in 
the  body  by  simply  spreading  out  flat  membranes.  Accord- 
ingly, in  most  cases,  a  large  area  is  obtained  by  folding  the 
secreting  surface  in  various  ways  so  that  a  wide  surface  can 
be  packed  in  a  small  bulk,  just  as  a  Chinese  paper  lantern 
when  shut  up  occupies  much  less  space  than  when  extended, 
although  the  actual  area  of  the  paper  in  it  remains  the  same. 
In  a  few  cases  the  folding  takes  the  form  of  protrusions  into 
the  cavity  of  the  secreting  organ  (C,  Fig.  45),  but  much 
more  commonly  the  surface  extension  is  attained  by  pitting  or 
depressing  the  supporting  or  basement  membrane,  covered  by 
its  epithelium  (2?) .  Such  a  secreting  organ  is  known  as  a 
true  gland. 


io8 


THE  HUMAN  BODY. 


FIG.  45. — Forms  of  glands.  A,  a  simple  secreting  surface;  a,  its  epithelium  ;  6, 
basement  membrane;  c,  capillaries  ;  B,  a  simple  tubular  gland  ;  C,  a  secreting  surface 
increased  by  protrusions  ;  JS,  a  simple  racemose  gland  ;  D  and  G,  compound  tubular 
glands  ;  f,  a  compound  racemose  gland.  In  all  but  A,  £,  and  C  the  capillaries  are 
omitted  for  the  sake  of  clearness.  //,  half  of  a  highly  developed  racemose  gland;  c, 
its  main  duct. 


FORMS   OF  GLANDS.  109 

Forms  of  Glands. — In  some  cases  the  surface  involutions 
are  uniform  in  diameter,  or  nearly  so  (#,  Fig.  45),  and  are 
known  as  tubular  ;  examples  are  found  in  the  lining  coat  of 
the  stomach  (Fig.  57),  also  in  the  skin  (Fig.  109)  where 
they  form  the  sweat-glands.  In  other  cases  the  involution 
swells  out  at  its  deeper  end  and  becomes  more  or  less  saccu- 
lated  (£);  such  glands  are  named  racemose  or  acinous.  The 
small  glands  of  the  skin  which  form  the  oily  matter  for  the 
hairs  (p.  227)  are  of  this  type.  In  both  kinds  the  lining 
cells  near  the  deeper  end  are  commonly  different  in  character 
from  the  rest,  and  around  that  part  of  the  gland  the  finest  and 
thinnest  walled  blood-vessels  {capillaries^  form  a  closer  net- 
work. These  deeper  cells  form  the  true  secreting  tissue  of 
the  gland,  while  the  tube,  lined  with  different  cells,  which 
leads  from  the  secreting  recesses  to  the  surface  on  which  the 
secretion  is  poured  out,  serves  merely  to  drain  it  off  and  is 
known  as  the  duct  of  the  .gland.  When  the  duct  is  undivided 
the  gland  is  simple  ;  but  when,  as  is  more  usual,  it  is  branched 
and  each  branch  has  a  true  secreting  chamber  at  its  end  the 
gland  is  compound,  tubular  (G),  or  racemose  (F,  H}  as  the 
case  may  be.  In  many  cases  the  chief  duct,  in  which  the 
smaller  ducts  unite,  is  of  considerable  length,  so  that  the  se- 
cretion is  poured  out  at  some  distance  from  the  main  mass  of 
the  gland. 

A  fully  formed  gland,  H,  is  thus  a  complex  structure,  con- 
sisting primarily  of  a  duct  (c)  ductules  (dd)  and  secreting  re- 
cesses (ee}.  The  ducts  and  ductules  are  lined  with  protective 
cells  which  differ  in  character  from  the  secreting  cells  lining 
the  deepest  parts.  The  cells  lining  the  ultimate  recesses  dif- 
fer in  different  glands,  and  produce  different  liquids  ;  conse- 
quently, though  all  glands  are  built  on  much  the  same  plan, 


no 


THE  HUMAN  BODY. 


m 


they  make  very  varied  secretions,  according  to  the  properties 
of  their  cells. 

The  Complexity  of  the  Alimentary  Canal. — We  may  now 

return  to  our  immediate  subject,  the  alimentary  canal.     This 

is  not  a  simple  tube,  but 
presents  several  dilatations  in 
its  course ;  nor  is  it  a  com- 
paratively straight  tube,  as 
diagrammatically  represented 
in  Fig.  i,  but,  being  much 
longer  than  the  body,  much 
of  it  is  packed  away  by  being 
coiled  up  in  the  abdominal 
cavity. 

Subdivisions  of  the  Ali- 
mentary Canal. — The  mouth 
opening  leads  into  a  chamber 
containing  the  teeth  and 
tongue,  named  the  mouth 
chamber  or  buccal  cavity. 
This  primary  dilatation  is 
separated  by  a  constriction 
(the  isthmus  of  the  fauces)  at 

FIG.     46.— The      mouth,     nose,      and  \ 

pharynx,    with     the    commencement    of  ,1        KooV  r»f  rVif  mniitVi     from 

the   gullet  and  larynx,    as   exposed  by   a  the     back  Ot    the  mOUth,    I) 
section,  a  little  to  the  left  of  the  median  ,  .  , 

plane  of  the  head,    a,  vertebral  column  ;  another    Cavity,     the 
6,   gullet  ;    <:,    windpipe  ;    </,    larynx  ;    <?, 


epiglottis  ;  f,  soft  palate  ;    ^,  opening  of 
Eustachian    tube  ;    k,     tongue  ;     /,   hard 


or  throat  chamber,  which  nar- 


palate  ;  m\  the  sphenoid  bone  on  the  base       TOWS  again    at    the  top    of   the 
of  the  skull ;  «,  the  fore  part  of  the  cra- 
nial cavity;   <?,/,  g,  the  turbinate  bones       neck    into    the     gullet   Or    (XSO- 
of    the   outer    side   of   the    left     nostril 

chamber.  phagus.     The  latter  runs  as  a 

comparatively  narrow  tube  through  the  thorax,  and  then, 
passing  through  the  diaphragm,  dilates  in  the  upper  part  of 
the  abdominal  cavity  to  form  the  stomach  (see  Fig.  i).  Be- 


THE  MOUTH  CAVTIY. 


ill 


yond  the  stomach  the  channel  again  narrows  to  form  a  long 
and  greatly  coiled  tube,  the  small  intestine,  which  terminates 
by  opening  into  the  large  intestine ;  this,  though  shorter,  is 
wider,  and  ends  by  opening  on  the  exterior. 

The  Mouth  Cavity  (Figs.  46  and  47)  is  bounded  in  front 
and  on  the  sides  by  the  lips  and  cheeks,  below  by  the  tongue 


FIG. 
pillar  o 


47. —  i,  soft  palate;    2,  its   median  ridge;    3,  uvula;  4,   anterior,    5,  posterior 
f  fauces  ;  6,  tonsil ;  7,  posterior  wall  of  pharynx  ;  8,  tongue. 


(k),  and  above  by  the  palate,  which  consists  of  an  anterior 
part  (/)  supported  by  bone  and  called  the  hard  palate,  and  a 
posterior  (_/")  containing  no  bone,  and  called  the  soft  palate. 
The  two  can  be  distinguished  by  applying  the  tip  of  the 
tongue  to  the  roof  of  the  mouth  and  drawing  it  backwards. 
The  hard  palate  forms  the  partition  between  the  mouth  and 
nose.  The  soft  palate  arches  down  at  the  back  of  the  mouth, 


H2  THE  HUMAN  BODY. 

hanging  like  a  curtain  between  it  and  the  pharynx,  as  can 
be  seen  on  holding  the  mouth  open  in  front  of  a  looking 
glass.  From  the  middle  of  its  free  border  a  conical  pro- 
cess, the  uvula,  hangs  down. 

The  Teeth. — Immediately  within  the  cheeks  and  lips 
are  two  semicircles,  formed  by  the  borders  of  the  upper  and 
lower  jaw-bones,  and  covered  by  the  gums,  except  at  inter- 
vals along  their  edges  where  teeth  are  implanted.  During 
life  two  sets  of  teeth  are  developed  :  the  first  or  milk  set  ap- 
pear soon  after  birth  and  are  shed  during  childhood,  when 
the  second  or  permanent  set  appear. 

The  General  Structure  of  a  Tooth.— The  teeth  differ  in 
minor  points  from  one  another,  but  in  all,  three  parts  are 
distinguishable  :  *  one,  seen  in  the  mouth  and  called  the 
crown  of  the  tooth;  a  second,  imbedded  in  the  jaw-bone 
and  called  the  root  or  fang  ;  and  between  the  two,  embraced 
by  the  edge  of  the  gum,  a  narrowed  portion,  the  neck  or 
cervix.  By  differences  in  their  forms  and  uses  the  teeth  are 
divided  into  incisors,  canines,  bicuspids,  and  molars,  arranged 
in  a  definite  order  in  each  jaw.  Beginning  at  the  middle 
line  we  find  in  each  half  of  each  jaw,  successively,  two  in- 
cisors, one  canine,  and  two  molars  in  the  milk  set,  making 
twenty  altogether  in  the  two  jaws.  The  teeth  of  the  per- 
manent set  are  thirty-two  in  number,  eight  in  each  half  of 
each  jaw,  viz. — beginning  at  the  middle  line — two  incisors, 
one  canine,  two  bicuspids,  and  three  molars.  The  bicuspids 
of  the  permanent  set  replace  the  molars  of  the'  milk  set, 
while  the  permanent  molars  are  new  teeth  added  as  the  jaw 
grows.  The  last  permanent  molars  are  often  called  the 
wisdom  teeth. 

*  A  number  of  teeth  can  be  readily  obtained  from  a  dentist,  and  will 
be  found  of  great  use  in  connection  with  this  lesson. 


CHARACTERS  AND  STRUCTURE  OF  TEETH.         113 

Characters  of  Individual  Teeth.. — The  incisors  or  cutting 
teeth  (Fig.  48)  are  adapted  for  cutting  the  food.  Their 
crowns  are  chisel-shaped  and  have  sharp  horizontal  cutting 
edges  which  become  worn  away  by  use,  so  that  they  are 
bevelled  off  at  the  back  in  the  upper  row  and  at  the  front  in 
the  lower.  Each  has  a  single  long  fang.  The  canines  (dog 
teeth}  (Fig.  49)  are  somewhat  larger  than  the  incisors. 
Their  crowns  are  thick  and  somewhat  conical,  having  a  cen- 
tral point  or  cusp  on  the  cutting  edge.  In  dogs  and  cats  the 
canines  are  very  long  and  pointed,  and  adapted  for  seizing 
and  holding  prey.  The  bicuspids  or premolars  (Fig.  50)  are 


FIG.  48.  FIG.  49.  FIG.  50.  FIG.  51. 

FIG.  48. — An  incisor  tooth. 
FIG.  49. — A  canine  or  eye  tooth. 

FIG.  50. — A  bicuspid  tooth  seen  from  its  outer  side  ;  the  inner  cusp  is  accordingly 
not  visible. 

FIG.  51. — A  molar  tooth. 

rather  shorter  than  the  canines  and  their  crowns  are  cuboidal. 
Each  has  two  cusps,  an  outer  and  an  inner.  The  molar  teeth 
or  grinders  (Fig.  51)  have  large  crowns  with  broad  surfaces, 
and  four  or  five  projecting  tubercles  which  roughen  them 
and  make  them  better  adapted  to  crush  the  food.  Each  has 
usually  several  fangs.  The  milk  teeth  differ  only  in  minor 
points  from  those  of  the  same  names  in  the  permanent  set. 

The  Structure  of  a  Tooth. — If  a  tooth  is  broken  open  a 
cavity  extending  through  both  crown  and  fang  will  be  found 
in  it.  This  is  filled  during  life  with  a  soft  pulp,  containing 
blood-vessels  and  nerves  and  known  as  the  "pulp  cavity." 


H4  THE  HUMAN  BODY. 

The  hard  parts  of  the  tooth  disposed  around  the  pulp  cavity 
consist  of  three  different  tissues.  Of  these,  one,  dentine  or 
ivory,  immediately  surrounds  the  cavity  and  makes  up  most 


FIG.  52.— Longitudinal  section  of  a  molar  tooth,     k,  crown  ;  »,  neck ;  _/j  fangs;  *, 
enamel  ;  </,  dentine  ;  c,  cement ;  /,  pulp  cavity. 

of  the  bulk  of  the  tooth  ;  covering  the  dentine  on  the  crown 
is  enamel,  the  hardest  tissue  in  the  body,*  and  on  the  fang 
the  cement,  which  is  a  thin  layer  of  bone. 

The  pulp  cavity  opens  below  by  a  narrow  aperture  at  the 
tip  of  the  fang,  or  at  the  tip  of  each  fang  if  the  tooth  has 
more  than  one.  Through  these  openings  its  blood-vessels 
and  nerves  enter. 

Hygiene  of  the  Teeth. — The  teeth  should  be  thoroughly 
cleansed  night  and  morning,  by  means  of  a  tooth-brush 
dipped  in  tepid  water.  Once  a  day  soap  should  be  used,  or  a 
*  Enamel  will  strike  fire  with  flint. 


THE   TONGUE.  115 

little  very  finely  powdered  chalk  sprinkled  on  the  brush.  The 
weak  alkali  of  the  soap  or  chalk  is  useful.  A  large  proportion 
of  a  tooth  consists  of  carbonate  and  phosphate  of  calcium, 
which  readily  dissolve  in  weak  acids ;  decomposing  food  par- 
ticles lodged  between  the  teeth  develop  acids,  which  eat 
away  the  tooth  slowly  but  surely.  Hence  all  food  particles 
should  be  carefully  removed  from  between  the  teeth ;  as  this 
cannot  always  be  effected  completely  it  is  important  to  brush 
the  teeth  with  alkaline  substances  which  will  neutralize  and 
render  harmless  any  acid.*  Good  manners  forbid  the  public 
use  of  a  tooth-pick,  but  on  the  earliest  privacy  after  a  meal  a 
wooden  or  quill  tooth-pick,  or  better  dental  silk,  should  be 
employed  systematically  and  carefully  to  dislodge  all  food 
remnants  which  may  have  remained  wedged  between  the 
teeth. 

Once  a  slight  cavity  has  been  formed,  the  process  of  decay 
is  apt  to  go  on  very  fast ;  first,  because  the  exposed  deeper 
layer  of  the  tooth  is  more  easily  dissolved  than  its  natural  sur- 
face, and  second,  because  the  little  pit  forms  a  lodging-place 
for  bits  of  food,  which,  in  decomposing  through  the  action  of 
bacteria,  form  acids  and  hasten  the  corrosion.  Small  eroded 
cavities  are  very  apt  to  be  overlooked ;  the  teeth  should, 
therefore,  be  thoroughly  examined  two  or  three  times  a  year 
by  a  dentist. 

The  Tongue  (Fig  53)  is  a  muscular  and  highly  movable 
organ,  covered  by  mucous  membrane  and  endowed  not  only 
with  a  delicate  sense  of  touch  but  with  the  sense  of  taste. 
Its  root  is  attached  to  the  hyoid  bone  (p.  20).  The  mucous 
membrane  covering  the  upper  surface  of  the  tongue  is  rough- 

*  Acid  medicines  should  always  be  sucked  through  a  glass  tube  and 
swallowed  with  as  little  contact  as  possible  with  the  teeth.  After  each 
dose  the  mouth  should  be  thoroughly  rinsed  with  water. 


n6  THE  HUMAN  BODY. 

ened  by  numerous  minute  elevations  or  papillce,  of  which 
there  are  three  varieties.      The  circumvallate  papilla  are  the 


FIG.  53. — The  upper  surface  of  the  tongue,     i,  2,  circumvallate  papillae ;  3,  fungi- 
form  papillae  ;  4,  filiform  papillae  ;  6,  mucous  glands. 

largest   and   fewest,  and  lie    near  the  root   of  the  tongue, 
arranged  in  the  form  of  a  V,  with  its  open  angle  turned  to- 


WHAT  A  "FURRED   TONGUE"   INDICATES.         nj 

wards  the  lips.  The  fungiform  papillce  are  rounded  masses 
attached  by  narrower  stems.  They  are  found  all  over  the 
middle  and  fore  part  of  the  upper  surface  of  the  tongue,  and 
during  life  are  readily  recognized  as  red  dots,  more  deeply 
colored  because  more  richly  supplied  with  blood  than  the  rest 
of  the  mucous  membrane.  The  filiform  papillce  are  pointed 
elevations  scattered  all  over  the  upper  surface  of  the  tongue, 
except  near  its  root.  On  our  tongues,  they  are  the  smallest 
and  most  numerous.* 

What  a  "Furred  Tongue"  Indicates. — In  health  the  sur- 
face of  the  tongue  is  moist,  covered  by  little  "  fur,"  and  in 
childhood  is  of  a  red  color.  In  adult  life  the  natural  color  of 
the  tongue  is  less  red,  except  around  the  edges  and  tip ;  a 
bright  red  glistening  tongue  is  then  usually  a  symptom  of 
disease.  When  the  digestive  organs  are  deranged  the  tongue 
is  commonly  covered  with  a  thick  yellowish  coat  and  there 
is  frequently  a  ' '  bad  taste  ' '  in  the  mouth,  f  All  the  parts  of 
the  alimentary  mucous  membrane  are  in  close  physiological 
connection,  and  anything  disordering  the  stomach  is  likely 
to  produce  a  "  furred  tongue,"  which  in  most  cases  may  be 
taken  as  indicating  something  wrong  with  the  deeper  parts  of 
the  digestive  tract. 

The  Salivary  Glands. — The  saliva,  which  is  poured  into 
the  mouth  and  moistens  it,  is  secreted  by  three  pairs  of 
glands,  the  parotid,  the  sublingual,  and  the  submaxillary. 

*  The  filiform  papillae  are  very  large  on  the  tongue  of  the  cat,  where 
they  may  readily  be  seen  and  felt.  They  are  large  in  nearly  all  car- 
onivrous  animals,  serving  to  scrape  or  lick  clean  bones,  etc.  Tamed 
tigers  have  been  known  to  draw  blood  by  licking  the  hand  of  their 
master. 

\  The  fur  of  the  tongue  consists  of  some  mucus,  a  few  cells  shed  from 
its  surface,  and  numerous  vegetable  microscopic  organisms  belonging  to 
the  group  of  Bacteria. 


us  THE  HUMAN  BODY. 

(Fig.  55.)  The  parotid  glands  lie  close  in  front  of  the  ear; 
each  sends  its  secretion  into  the  mouth  by  a  duct,  which  opens 
inside  the  cheek  opposite  the  second  upper  molar  tooth.  In 
the  disease  known  as  mumps  *  the  parotid  glands  are  inflamed 
and  enlarged.  The  sublingual  glands  lie  under  the  tongue 


FIG.  55. — The  salivary  glands.     One  side  of  the  lower  jaw  has  been  removed,  and 
the  face  dissected,  in  order  to  show  the  salivary  glands  of  the  right  side. 

between  the  halves  of  the  lower  jaw-bone,  and  their  ducts 
open  in  the  front  of  the  mouth  beneath  the  tongue.     The  sub- 

*  Technically,  parotitis. 


THE  FAUCES— THE  PHARYNX.  Jt$ 

maxillary  glands  lie  beneath  the  floor  of  the  mouth  behind 
the  sublingual  near  the  angle  of  the  jaw. 

The  Fauces  is  the  name  given  to  the  passage  which  can 
be  seen  at  the  back  of  the  mouth  leading  from  it  into  the 
pharynx,  below  the  soft  palate.*  It  is  bounded  above  by  the 
soft  palate  and  the  uvula,  below  by  the  root  of  the  tongue, 
and  on  the  sides  by  muscles,  covered  by  mucous  membrane 
and  reaching  from  the  soft  palate  to  the  tongue.  The  mus- 
cles cause  folds  known  as  the  pillars  of  the  fauces.  Each  fold 
divides  near  the  tongue,  and  in  the  hollow  between  its  divi- 
sions lies  a  tonsil  (Fig.  53),  a  soft  rounded  body  about  the 
size  of  an  almond  containing  numerous  minute  glands  which 
form  mucus. 

Enlarged  Tonsils. — The  tonsils  sometimes  become  en- 
larged during  a  cold  or  sore  throat.  Occasionally  the 
enlargement  is  permanent  and  causes  much  annoyance. 
The  tonsils  can,  however,  be  readily  removed  without 
danger,  and  this  is  the  treatment  usually  adopted  in  such 
cases. 

The  Pharynx  or  Throat  Cavity  (Fig.  46). — This  portion 
of  the  alimentary  canal  may  be  described  as  a  conical  bag 
with  its  broad  end  turned  up  toward  the  base  of  the  skull  and 
the  other  end  narrowed  into  the  gullet.  Its  front  or  ventral 
wall  is  imperfect,  presenting  apertures  which  lead  into  the 
nose,  the  mouth,  and  (through  the  larynx  and  windpipe) 
into  the  lungs.  Except  when  food  is  being  swallowed  the 
soft  palate  hangs  down  between  the  mouth  and  pharynx ; 
during  swallowing  (deglutition}  it  is  raised  into  a  horizontal 
position,  and  separates  the  upper  or  nasal  portion  of  the 
pharynx  from  the  rest.  Through  this  upper  part  only  air 

*  Observe  for  yourself  with  the  help  of  a  looking  glass. 


120  THE  HUMAN  BODY. 

passes,*  entering  it  from  the  posterior  ends  of  the  two  nos- 
tril chambers.  Through  the  lower  portion  both  food  and 
air  pass,  one  on  its  way  to  the  gullet  (b,  Fig.  46),  the  other 
through  the  larynx  (d)  to  the  windpipe  (c\  When  a  morsel 
of  food  "goes  the  wrong  way"  it  takes  the  latter  course. 
Opening  into  the  upper  portion  of  the  pharynx  on  each  side 
is  an  Eustachian  tube  (g).  At  the  root  of  the  tongue,  over 
the  opening  of  the  larynx,  is  a  plate  of  cartilage,  the  epiglottis 
(e),  which  can  be  seen  if  the  mouth  is  widely  opened  and  the 
back  of  the  tongue  pressed  down  by  the  handle  of  a  spoon. 
During  swallowing  the  epiglottis  is  pressed  down  like  a  lid 
over  the  opening  of  the  air-tube  and  helps  to  keep  food  from 
entering  it.  The  pharynx  is  lined  by  mucous  membrane  and 
has  muscles  in  its  walls  which,  by  their  contraction,  drive 
the  food  on. 

The  (Esophagus  or  Gullet  is  a  tube  which  commences  at 
the  lower  termination  of  the  pharynx  and,  passing  on  through 
the  neck  and  chest,  ends  below  the  diaphragm  in  the  stom- 
ach. In  the  neck  it  lies  close  behind  the  windpipe, 

The  Stomach.  (Fig.  56)  is  a  curved  conical  elastic  bag 
placed  transversely  in  the  upper  part  of  the  abdominal  cav- 
ity, f  Its  larger  end  is  turned  to  the  left  and  lies  close  be- 
neath the  diaphragm  ;  the  gullet  (d)  opens  into  its  upper 
border,  through  the  cardiac  orifice  at  a.  The  narrower  right 
end  is  continuous  with  the  small  intestine  and  communicates 

*  During  a  severe  attack  of  vomiting  the  soft  palate  often  acts 
imperfectly  in  closing  the  passage  between  gullet  and  nostrils  ;  hence 
some  of  the  ejected  matter  not  unfrequently  is  expelled  through  the  noser 

f  The  general  anatomical  arrangement  of  the  stomach,  and  its  con- 
nections with  the  gullet  and  intestine,  may  be  readily  shown  on  the  body 
of  a  puppy,  kitten,  or  rat  which  has  been  killed  by  placing  it  for  five 
minutes  in  a  small  box  containing  also  a  sponge  soaked  with  chloroform. 


THE  STOMACH. 


121 


with  it  through  the  pyloric  orifice  (c).  The  pylori  c  end  of 
tne  stomach  is  separated  from  the  diaphragm  by  the  liver 
(see  Fig.  4).  When  moderately  distended  the  stomach  is 
about  twelve  inches  long,  four  inches  across  at  its  widest 
part,  and  contains  about  three  pints. 

The  Glands   of  the  Stomach. — The   mucous   membrane 


FIG.  56.— The  stomach.  <t,  lower  end  of  the  gullet ;  a,  position  of  the  cardiac 
aperture  ;  £,  the  fundus ;  r,  the  pylorus  ;  e,  the  first  part  of  the  small  intestine  ;  along 
</,  6,  <r,  the  great  curvature  ;  between  the  pylorus  and  d,  the  lesser  curvature. 


FIG.  57. — A  thin  section  through  the  gastric  mucous  membrane,  perpendicular  to 
its  surface,  magnified  about  25  diameters,  a,  a  simple  peptic  gland ;  b,  a  compound 
peptic  gland  ;  <:,  a  mucous  gland. 

lining  the  stomach  is  seen,  with  a  magnifying  glass,  to  be 
covered  with  shallow  pits.  A  microscope  shows  on  the  bot- 
tom of  each  of  these  pits  the  openings  of  several  minute  tubes, 


122 


THE  HUMAN  BODY. 


Mm 


Sub- 
Mucous 
coat 


the  gastric  glands,  which  lie  imbedded  in  the   mucous  mem- 
brane (Figs.  57  and  58)  and  secrete  the  gastric  juice. 

The  Muscular  Goat  of 
the  Stomach  lies  outside 
the  mucous  membrane,,  and 
is  made  up  (Fig.  34  and 
Fig.  480)  of  plain  muscular 
tissue,  whose  fibres  run  in 
different  directions.  By  its 
contractions  it  stirs  up  the 
food  and  mixes  it  with  the 
gastric  juice.  Around  the 
pyloric  orifice  of  the  stom- 
ach is  a  thick  ring  of  mus- 
cle (the  pyloric  sphincter}, 
which  usually  by  contract- 
ing closes  the  passage  be- 
tween the  stomach  and 
the  commencement  of  the 
small  intestine.  During 
digestion  in  the  stomach 

pylorjc      sphincter     TC- 

laxes    from    time    to    time, 

and  allows  food,  more  or  less  digested,  to  pass  on  into  the 
intestine. 

Palpitation  of  the  Heart. — The  cardiac  end  of  the  stom- 
ach lies  close  below,  and  the  heart  immediately  above,  the 
diaphragm.  Over-distension  of  the  stomach  by  gas  {flatu- 
lence}, which  is  one  of  the  symptoms  accompanying  indiges- 
tion, may  press  up  the  diaphragm  and  interfere  with  the 
proper  working  of  the  thoracic  organs,  causing  feelings  of 
oppression  in  the  chest,  or  palpitation  of  the  heart, 


Serosa 


FIG.   58. — Wall  of  human  stomach.     .£",  epi- 
thelium ;  G,  glands  ;  Mm,  muscularis  mucosse.  • 


SMALL  INTESTINE. 


123 


The  Small  Intestine  commences  at  the  pylorus  and  ends, 
after  many  windings,  in 
the  large  intestine.  It  is 
about  twenty  feet  (six 
meters)  long  and  about 
two  inches  (five  centi- 
meters) wide  at  its  gastric 
end,  narrowing  to  about 
two  thirds  of  that  width  at 
its  lower  portion.  Exter- 
nally there  are  no  lines  of 
subdivision  on  the  small 
intestine,  but  anatomists 
arbitrarily  describe  it  as 
consisting  of  three  parts, 
of  which  the  first  ten  or 
twelve  inches  is  the  duo- 
denum* the  succeeding 
two  fifths  of  the  remainder 
the  jejunum,  and  the  rest 
the  ileum. 

The  Mucous  Coat  of  the 

Small    Intestine     is    pink, "pyloric'endof  the  stomach;  Z>,  the  duodenum; 

J,  /,  the  convolutions  of  the  small  intestine;  CC, 

<?nff       anrl     pvtremplv     va<;    ^e  caecum  with  the  vermiform  appendix;   AC, 
Ml»      '  ieV      VaS     ascending,  TC,  transverse,  and  DC,  descending 

cular.  Throughout  a  great  colon;  *• the  rectum- 
portion  of  the  length  of  the  tueb  it  is  raised  into  permanent 
folds  in  the  form  of  crescentic  ridges  (Fig.  60).  These  folds 
(valvulce  conniventes)  run  transversely  for  a  greater  or  less 
distance  round  the  intestine.  They  are  first  found  about  two 
inches  from  the  pylorus,  and  are  most  thickly  set  and  largest 

*  Duodenum  signifies  literally  twelve,  and  is  applied  here  because  this 
portion  is  about  twelve  finger-breadths  long. 


FIG.  59. — Diagram  of  abdominal  part  of  ali- 
.  mentary  canal.      C,   the    cardiac,    and    />,   the 


"4  THE  HUMAN  BODY. 

in  the  upper  half  of  the  jejunum.  In  the  lower  half  they 
become  gradually  less  conspicuous,  and  finally  disappear 
altogether  about  the  middle  of  the  ileum.  The  folds  of  the 


FIG.  60. — A  portion  of  the  small  intestine  opened  to  show  the  valvulce  conniventes. 

mucous  membrane  serve  greatly  to  increase  its  surface  both 
for  absorption  and  secretion,  and  also  to  delay  the  food  in  its 
passage ;  it  collects  in  the  hollows  between  them,  and  so  is 
longer  exposed  to  the  action  of  the  digestive  liquids. 

The  Villi. — Examined  closely  with  the  eye  or,  better, 
with  a  hand  lens,  the  mucous  membrane  of  the  small  intestine 
is  seen  to  be  shaggy  and  covered  everywhere  (both  over  the 
valvulae  conniventes  and  between  them)  with  closely  packed 
minute  elevations  standing  up  somewhat  like  the  "pile"  on 
velvet  and  known  as  the  villi  (Fig.  61).  In  structure  a  villus 
is  somewhat  complex.  BeneatL  the  covering  of  a  single  layer 
of  cells  the  villus  consists  of  a  framework  of  connective 
tissue  supporting  the  more  essential  constituents.  Near  the 
surface  is  a  network  of  plain  muscular  tissue.  In  the  centre 
is  an  offshoot  of  the  lymphatic  or  absorbent  system,  sometimes 
in  the  form  of  a  single  vessel  with  a  closed  dilated  end,  and 
sometimes  as  a  network  formed  by  two  main  vessels  with 
cross-branches.  During  digestion  these  lymphatics  are  filled 
with  a  milky  white  liquid  absorbed  from  the  intestines,  and 
are  accordingly  called  the  lacteals.  They  communicate  with 
larger  branches  in  the  outer  coats  of  the  intestine,  which 


VILLI,   GLANDS,  ETC.,   OF  SMALL  INTESTINE.        125 

unite  to  form  the  trunks  of  the  main  lymphatic  system. 
Finally,  in  each  villus,  outside  its  lacteals  and  beneath  its 
muscular  layer,  is  a  close  network  of  blood-vessels. 


FIG.  61. — Villi  of  the  small  intestine,  magnified  about  80  diameters.  In  the  left- 
hand  figure  the  lacteals,  #,  3,  <r,  are  filled  with  white  injection;  d,  blood-vessels.  In 
the  right-hand  figure  the  lacteals  alone  are  represented,  filled  with  a  dark  injection. 
The  epithelium  covering  the  villi,  and  their  muscular  fibres  are  omitted. 

The  Glands  of  the  Small  Intestine  open  on  the  surface 
of  the  small  intestine  between  the  bases  of  the  villi  and  are 
called  the  crypts  of  Lieberkuhn  (Fig.  62).  Each  is  a  simple 
unbranched  tube,  lined  by  a  single  layer  of  cells. 

The  Muscular  Coat  of  the  Small  Intestine,  lying  outside 
the  mucous  coat,  is  composed  of  plain  muscular  tissue,  dis- 
posed in  two  layers,  an  inner  circular  and  an  outer  longi- 
tudinal. By  their  combined  and  alternating  contractions 
they  produce  annular  constrictions  of  the  intestine,  which 
slowly  travel  from  the  stomach  downward,  one  after  another, 
and  thereby  force  the  digesting  food  along  the  tube.  This 
movement  is  called  peristalsis. 

The  Large  Intestine  (Fig.  59),  forming  the  final  portion 


126 


THE  HUMAN  BODY. 


of  the  alimentary  canal,  is  about  5  feet  (1.5  meters)  long, 
and  varies  in  diameter  from  2^  to  i£  inches  (6-4  centimeters). 
Anatomists  describe  it  as  consisting  of  the  ccecum  (cc)  with 
its  vermiform  appendix,  the  colon  (AC,  TC,  DC),  and  the  rectum 

A 


FIG.  62. — Vertical  section  of  the  intestinal  mucous  membrane  of  the  rabbit.  Two 
villi  are  represented,  in  one  of  which  the  dilated  lacteal  alone  is  shown,  in  the  other 
the  blood  vessels  and  lacteal  are  both  seen  injected,  the  lacteal  white,  the  blood 
vessels  dark  ;  a.  the  lacteal  vessels  of  the  yilli ;  a',  horizontal  lacteal,  which  they  join  ; 
b,  capillary  blood  vessels  in  one  of  the  villi;  c,  small  artery;  d,  vein;  e,  the  epithe- 
lium covering  the  villi ;  g ,  tubular  glands  or  crypts  of  Lieberkiihn,  some  divided  down 
the  middle,  others  cut  more  irregularly  ;  z",  the  submucous  layer.  A,  cross-section  of 
three  tubular  glands  more  highly  magnified. 

(R).  The  small  intestine  opens  into  the  side  of  the  large, 
some  distance  from  its  closed  end ;  the  caecum  is  that  part  of 
the  large  intestine  which  extends  beyond  the  communication. 
From  it  projects  the  vermiform  appendix,  a  narrow  tube  not 
thicker  than  a  lead  pencil,  and  about  4  inches  (10  centi- 
meters) long.  It  is  a  residual  structure  of  considerable 
importance  in  some  of  the  lower  animals.  Its  contents  are 
ordinarily  the  same  as  those  of  the  caecum.  It  is  therefore 
frequently  the  receptacle  of  grape  seeds,  etc.,  which  appar- 
ently do  no  harm.  It  is  sometimes  the  seat  of  an  inflammation 


LARGE  INTESTINE— ILEO-CAECAL   VALVE. 


127 


(appendicitis)  due  to  bacterial  activity  under  favoring  con- 
ditions. The  colon  commences  on  the  right  side  of  the 
abdominal  cavity  where  the  small  intestine  communicates  with 
the  large,  runs  up  for  some  distance  on  that  side  (ascending 
colon),  then  crosses  the  middle  line  (transverse  colon)  below 
the  stomach,  and  turns  down  (descending  colon)  on  the  left  side. 
In  the  lower  left  side  of  the  abdomen  it  makes  an  S-shaped 


FIG.  63. — The  ileo-caecal  valve,  a,  ileum  ;  b,  ascending  colon  ;  c,  caecum  ;  </,  junc- 
tion of  the  caecum  and  colon  ;  e  and  _/~,  loose  folds  of  the  mucous  membrane,  forming 
the  ileo-caecal  valve  ;  &,  vermiform  appendage. 

bend  known  as  the  sigmoid  flexure  ;  from  this  the  rectum  pro- 
ceeds to  the  opening  by  which  the  intestine  communicates 
with  the  exterior.  The  mucous  coat  of  the  large  intestine 
possesses  no  villi  nor  valvulae  conniventes  ;  it  contains  numer- 
ous closely  set  glands  much  like  the  crypts  of  Lieberkiihn. 

The  Ileo-csecal  Valve. — Where  the  small  intestine  joins 
the  large,  there  is  a  valve  formed  by  two  flaps  of  the  mucous 
membrane  sloping  down  into  the  colon,  and  so  arranged  as 
to  allow  matters  to  pass  readily  from  the  ileum  into  the  large 
intestine,  but  not  the  reverse  way. 


128 


THE  HUMAN  BODY. 


The  Liver. — Besides  the  secretions  formed  by  the  glands 
'imbedded  in  its  walls,  the  small  intestine  receives  those  of 
two  large  glands,  the  liver  and  pancreas,  which  lie  in  the 
atdominal  cavity.  The  ducts  of  both  open,  by  a  common 
aperture,  into  the  duodenum  about  4  inches  (10  centi- 
meters) from  the  pylorus. 

The  liver  is  the  largest  gland  in  the  body,  weighing  from 
50  to  60  ounces  (1400  to  1700  grams).  It  is  situated  in 
Vf  ,  a.  Lt 


Deli 


Lv 


FIG.  64.— The  under  surface  of  the  liver,  d,  right,  and  s,  left  lobe ;  Vh,  hepatic 
vein;  Vp,  portal  vein;  Vc,  vena  cava  inferior;  Dch,  common  bile  duct;  DC,  cystic  duct; 
Dh,  hepatic  duct;  Vf,  gall  bladder. 

the  upper  part  of  the  abdominal  cavity  (!e,  Ie',  Fig.  4), 
rather  more  on  the  right  than  on  the  left  side,  immediately 
below  the  diaphragm.  The  liver  is  of  dark  reddish-brown 
color,  and  of  soft  friable  texture.  The  vessels  carrying 
blood  to  the  liver  (Fig.  64)  are  the  portal  vein  (Vp),  and 
the  hepatic  artery ;  both  enter  it  at  a  groove  on  its  under 
side,  where  a  duct  also  passes  out  from  each  half  of  the 
organ.  The  ducts  unite  to  form  the  hepatic  duct 


THE  LIVER. 


129 


which  meets  the  cystic  duct  (Dc},  proceeding  from  the  gall- 
bladder (fJO,   a  pear-shaped  sac  in  which  the  bile  or  gall 
V  U 


FIG.  65. — The  stomach,  pancreas,  liver,  and  duodenum,  with  part  of  the  rest  of  the 
small  intestine  and  the  mesentery;  the  stomach  and  liver  have  been  turned  up  so  as 
to  expose  the  pancreas.  K,  stomach;  Z>,  D' ',  Z>",  duodenum;  Z,,  spleen;  /»,  pancreas; 
J?,  right  kidney;  7',  jejunum;  Vf,  gall  bladder;  A,  hepatic  duct;  c,  cystic  duct;  ch, 
common  bile  duct;  i,  aorta;  2,  an  artery  (left  coronary)  of  the  stomach;  3,  hepatic 
artery;  4,  splenic  artery;  5,  superior  mesenteric  artery;  6,  superior  mesenteric  vein; 
7,  splenic  ve.n;  Vp^  portal  vein. 

formed  by  the  liver  accumulates  when  food  is  not  being  di- 
gested in  the  intestine.    The  common  bile  duct  {Dch),  formed 


THE  HUM4N  BODY. 

by  the  union  of  the  hepatic  and  cystic  ducts,  opens  into  the 
duodenucu. 

The  Functions  of  the  Liver. — The  size  of  the  liver  sug- 
gests that  it  has  important  functions  in  the  body.  It  re- 
ceives all  the  blood  from  the  stomach  and  intestines  (the 
portal  system).  Its  cells  destroy  old  red  corpuscles.  They 
also  take  out  of  the  blood  excess  of  sugar  and  store  it  up  in 
the  form  of  a  kind  of  animal  starch  (glycogen},  which  they 
later  dole  out  again  as  sugar  when  the  blood  needs  it.  Ex- 
periments suggest  that  the  liver  cells  bring  about  the  final 
oxidation  of  nitrogenous  materials  into  urea,  in  which  form 
they  are  excreted  by  the  kidneys. 

The  Pancreas  *  is  a  compound  racemose  gland.  It  is  an 
elongated  soft  organ  of  a  pinkish-yellow  color,  lying  along 
the  lower  border  of  the  stomach.  Its  right  end  is  embraced 
by  the  duodenum,  which  there  makes  a  curve  to  the  left.  A 
duct  drains  it  and  joins  the  common  bile  duct  close  to  its 
intestinal  opening.  The  pancreas  secretes  a  watery-looking 
liquid,  much  like  saliva  in  appearance,  which  is  of  great 
importance  in  digestion. 

*  Butchers  sell  two  kinds  of  sweetbread,  known  as  the  belly  sweetbread 
and  the  neck  or  heart  sweetbread.  The  former  is  the  pancreas;  the 
latter  is  the  thymus,  an  organ  of  doubtful  function,  found  only  in  young 
animals,  and  lying  at  the  bottom  of  the  neck  and  upper  part  of  the  chest 
in  front  of  the  windpipe. 


CHAPTER  XII. 
DIGESTION. 

The  Object  of  Digestion. — A  few  of  the  foodstuffs  which 
we  eat  arc  in  solution  and  ready  to  soak  at  once  into  the 
lymphatics  and  blood  vessels  of  the  alimentary  canal;  others, 
such  as  a  grain  of  salt,  though  not  dissolved  when  put  into 
the  mouth,  are  readily  soluble  in  the  liquids  found  in  the 
alimentary  canal  and  need  no  further  digestion.  In  the  case 
of  many  most  important  foodstuffs,  however,  as  milk,  special 
chemical  changes  have  to  be  brought  about  to  make  them 
capable  of  absorption.  The  different  secretions  poured  into 
the  alimentary  tube  act  in  various  ways  upon  different  food- 
stuffs, dissolving  some  and  chemically  changing  others,  until 
at  last  all  are  in  a  condition  in  which  they  can  be  taken  up 
into  the  lymph  and  blood-vessels  for  transference  to  distant 
parts  of  the  body. 

Digestive  Ferments. — The  chemical  changes  necessary  to 
make  the  foods  absorbable  are  accomplished  almost  wholly 
by  the  action  of  various  organic  ferments,  each  with  a  special 
power  adapted  to  the  digestion  of  a  particular  foodstuff. 
Ptyalin,  found  in  saliva,  pepsin  and  rennin  in  gastric  juice, 
trypsin,  amylopsin,  and  steapsin  in  the  pancreatic  juice,  and 
invertin  in  the  intestinal  juice,  are  the  most  important  of 
these. 

The  Saliva,  the  first  solvent  poured  upon  the  food,  is  a 
mixture  of  pure  saliva  from  the  salivary  glands  with  the 

131 


I32  THE  HUM4N  BODY. 

mucus  secreted  by  the^  membrane  lining  the  mouth.  This 
mixed  saliva  is  a  colorless,  cloudy,  feebly  alkaline  liquid. 

The  Uses  of  Saliva  are  mainly  physical  and  mechanical. 
It  keeps  the  mouth  moist  and  allows  us  to  speak  with  com- 
fort. Most  young  orators  know  the  distress  occasioned  by 
the  suppression  of  the  salivary  secretion  through  nervous- 
ness, and  the  imperfect  efficacy  under  such  circumstances  of 
the  traditional  glass  of  water  placed  beside  public  speakers. 
The  saliva  also  enables  us  to  swallow  dry  food ;  such  a  thing 
as  a  cracker  when  chewed  would  give  rise  merely  to  a  heap 
of  dust,  impossible  to  swallow,  were  not  the  mouth  cavity 
kept  moist.*  The  saliva  further  dissolves  such  bodies  as 
salt  and  sugar  when  taken  into  the  mouth  in  a  solid  form, 
and  enables  us  to  taste  them ;  undissolved  substances  are  not 
tasted,  a  fact  which  any  one  can  verify  for  himself  by  wiping 
his  tongue  dry  and  placing  a  fragment  of  sugar  upon  it. 

Chemical  Action  of  the  Saliva. — In  addition  to  these  phy- 
sical actions,  the  saliva  effects  a  chemical  change  on  an  im- 
portant foodstuff,  due  to  the  presence  of  the  ferment  ptyalin. 
Starch  (although  it  swells  up  greatly  in  hot  water)  is  insoluble 
and  cannot  be  absorbed  from  the  alimentary  canal.  Ptyalin 
adds  chemically  a  portion  of  water  to  the  starch  and  thus 
changes  it  into  the  readily  soluble  and  absorbable  maltose,  a 
form  of  sugar. 

ZC.Hl.O.-i-2H,0=2C.H,,0.- 

Starch.  Water.  Maltose. 

*  This  fact  used  to  be  taken  advantage  of  in  the  East  Indian  rice 
ordeal  for  the  detection  of  criminals.  The  guilty  person,  believing 
firmly  that  he  cannot  swallow  the  parched  r'~e  given  him,  and  sure  of 
detection,  is  apt  to  have  his  salivary  glands  paralyzed  by  fear,  and  so 
does  actually  become  unable  to  swallow  the  rice;  while  in  those  with 
clear  consciences  the  nervous  system,  acting  normally,  excites  the  usual 
reflex  secretion,  and  the  dry  food  causes  no  difficulty  of  deglutition. 


SWALLOWING  OR  DEGLUTITION.  133 

The  Influence  of  Saliva  in  Promoting  Digestion  in  the 
Stomach. — It  changes  starch  into  maltose  most  rapidly  when 
no  acid  is  present.  When  the  food  passes  from  the  mouth  to 
the  stomach  the  saliva's  action  is  retarded  by  the  acidity  of 
the  gastric  juice.  Indirectly,  however,  the  saliva  promotes 
digestion  in  the  stomach.  Weak  alkalies  stimulate  the  gastric 
glands  to  pour  forth  more  abundant  secretion,*  and  the  alka- 
line saliva  acts  in  this  way.  This  is  one  reason  why  food 
should  be  well  chewed  before  being  swallowed;  its  taste,  and 
the  movements  of  the  jaws,  excite  a  more  abundant  salivary 
secretion,  and  the  saliva,  when  swallowed,  helps  to  stimulate 
the  stomach. 

Swallowing  or  Deglutition. — A  mouthful  of  solid  food  is 
broken  up  by  the  teeth  and  rolled  about  the  mouth  by  the 
tongue  until  it  is  thoroughly  mixed  with  saliva  and  made  into 
a  soft  pasty  mass.  The  muscles  of  the  cheeks  keep  it  from 
getting  between  them  and  the  gums.f  The  mass  is  finally  sent 
on  from  the  mouth  to  the  stomach  by  the  process  of 'deglutition, 
which  occurs  in  three  stages.  The  first  stage  includes  the 
passage  from  the  mouth  into  the  pharynx.  The  food  being 
collected  into  a  heap  on  the  tongue,  the  tip  of  that  organ  is 
placed  against  the  front  of  the  hard  palate,  and  then  the  rest 
of  the  tongue  is  raised  from  before  back,  so  as  to  compress 
the  food  mass  between  it  and  the  palate  and  drive  it  through 
the  fauces.  This  much  of  the  act  of  swallowing  is  voluntary, 
or  at  least  is  under  the  control  of  the  will,  although  it  com- 
monly takes  place  unconsciously.  The  second  stage  of  deglu- 
tition is  that  in  which  the  food  passes  through  the  pharynx ; 

*  Hence  the  efficacy  of  a  little  carbonate  of  soda  or  apollinaris  water 
taken  before  meals,  in  some  forms  of  dyspepsia. 

f  Persons  with  facial  paralysis  have  from  time  to  time  to  press  out 
with  the  finger  food  which  has  collected  outside  the  gums,  where  it  can 
neither  be  chewed  nor  swallowed. 


134  THE  HUMAN  BODY. 

this  is  the  most  rapid  part  of  its  progress,  since  the  pharynx 
has  to  be  emptied  quickly  so  as  to  clear  the  opening  of  the  air- 
passages  for  breathing  purposes.  The  food  mass,  passing 
back  over  the  root  of  the  tongue,  pushes  down  the  epiglottis; 
at  the  same  time  the  larynx  (or  voice-box  at  the  top  of  the 
windpipe)  rises  to  meet  the  epiglottis,  and  thus  aids  in  closing 
the  passage  to  the  lungs.*  The  soft  palate  is  raised  at  the 
same  time  to  close  the  passage  into  the  nose  (see  Fig.  46). 
As  the  final  step  the  isthmus  of  the  fauces  is  closed  as  soon 
as  the  food  has  passed,  by  the  contraction  of  the  muscles  on 
its  sides  and  the  elevation  of  the  root  of  the  tongue.  As  all 
passages  out  of  the  pharynx  except  the  gullet  are  thus  blocked, 
the  pharyngeal  muscles,  by  contracting,  can  squeeze  the  food 
only  into  the  oesophagus.  The  muscular  movements  concerned 
in  this  part  of  deglutition  are  all  excited  without  the  interven- 
tion of  the  will ;  the  food,  by  touching  the  mucous  membrane 
of  the  pharynx,  produces  involuntarily  the  proper  action  of 
the  swallowing  muscles,  f  Indeed,  many  persons  after  having 
got  the  mouth  completely  empty  cannot  perform  the  move- 
ments of  the  second  stage  of  deglutition  at  all.  On  account 
of  the  involuntary  nature  of  the  contractions  of  the  pharynx 
the  isthmus  of  the  fauces  forms  a  sort  of  Rubicon  ;  food  that 
has  entered  the  pharynx  must  be  swallowed,  even  though  the 
shallower  learns  immediately  that  he  is  taking  poison.  The 
third  stage  of  deglutition  is  that  in  which  the  food  is  passing 
along  the  gullet,  and  is  comparatively  slow.  Even  liquid  sub- 
stances do  not  fall  or  flow  down  this  tube,  but  have  their  pas- 
sage more  or  less  controlled  by  its  muscular  coats,  which  grip 

*  The  raising  of  the  larynx  during  swallowing  can  be  readily  felt  by 
placing  the  finger  on  its  large  cartilage  forming  "Adam's  apple  "  in  the 
neck. 

\  The  process  is  what  is  known  as  a  reflex  action.     See  Chap.  XX. 


GASTRIC  JUICE-PEPTONES.  135 

the  successive  portions  swallowed  and  pass  them  on.  Hence 
the  possibility  of  performing  the  apparently  wonderful  feat  of 
drinking  a  glass  of  water  while  standing  upon  the  head  :  peo- 
ple forget  that  one  sees  the  same  thing  done  every  day  by 
horses  and  other  animals  which  drink  with  the  pharyngeal  end 
of  the  gullet  lower  than  the  stomach. 

The  Gastric  Juice. — The  food  having  entered  the  stomach 
is  exposed  to  the  action  of  the  gastric  juice,  which  is  a  thin 
colorless  or  pale  yellow  liquid  of  a  strongly  acid  reaction.  It 
contains,  beside  water,  salts  and  mucus,  free  hydrochloric  acid 
(about  0.2  per  cent),  and  a  ferment  pepsin,  which  in  acid  liq- 
uids has  the  power  of  converting  ordinary  proteids  into  closely 
allied  substances  called  peptones.  It  also  dissolves  solid  pro- 
teids, changing  them  at  the  same  time  into  peptones. 

Peptones. — Ordinary  proteids  are  typical  examples  of 
what  are  called  "colloids,"  that  is  to  say,  substances  which 
do  not  readily  pass  through  moist  animal  membranes.  Pep- 
tones are  a  kind  of  proteid  which  does  readily  pass  through 
such  membranes,  and  are,  therefore,  capable  of  absorption 
from  the  alimentary  canal.  (See  Dialysis,  p.  145.) 

The  change  to  peptone  is  solely  for  the  purpoes  of  absorp- 
tion, since  peptone  is  not  found  in  the  blood,  and  when  in- 
troduced acts  as  a  poison.  Peptone  is  chiefly  represented  in 
the  blood  by  the  blood  proteids  serum,  albumin  and  serum 
globulin.  This  change  from  the  diffusible  peptone  back  to  a 
non-diffusible  proteid  is  supposed  to  be  due  to  the  action  of 
the  epithelial  cells  of  the  intestine  through  which  the  absorp- 
tion takes  place.  It  is  thus  seen  that  the  digestion  of  pro- 
teids is  but  a  step  toward  the  production  of  the  proteids  of 
the  blood,  which  form  the  real  nitrogenous  food  of  the  tissue. 

Gastric  Digestion. — In  the  stomach  the  onward  progress 
of  the  food  is  stayed  for  some  time.  The  pyloric  sphincter 


136  THE  HUM  AH  BODY. 

remaining  contracted  closes  the  aperture  leading  into  the 
intestine,  and  the  irregularly  disposed  muscular  layers  of  the 
stomach  keep  its  semi -liquid  contents  in  constant  movement, 
by  which  all  portions  are  thoroughly  mixed  with  the  secre- 
tion of  its  glands.  In  the  stomach,  part  of  the  proteid  of  the 
food  is  dissolved  and  turned  into  peptones.  Certain  mineral 
salts  (as  phosphate  of  lime,  of  which  there  is  always  some  in 
bread),  which  are  insoluble  in  water  but  soluble  in  dilute 
acids,  are  also  dissolved  in  the  stomach.  On  the  other  hand, 
the  gastric  juice  has  no  action  upon  starch,  nor  does  it  digest 
oily  substances.  By  the  solution  of  the  white  fibrous  con- 
nective tissues  the  disintegration  of  animal  foods,  commenced 
by  the  teeth,  is  carried  much  further  in  the  stomach ;  and 
the  food  mass,  mixed  with  much  gastric  secretion,  becomes 
reduced  to  the  consistency  of  a  thick  soup,  usually  of  a  gray- 
ish color.  In  this  state  it  is  called  chyme. 

The  Chyme  contains,  after  an  ordinary  meal,  a  consid- 
erable quantity  of  peptones,  which  are  in  part  gradually 
absorbed  into  the  blood  and  lymphatic  vessels  of  the  gastric 
mucous  membrane  and  carried  off,  along  with  other  dissolved 
and  dialyzable  bodies,  e.g.  salts  and  sugar.  After  the  food 
has  remained  in  the  stomach  some  time  (one  and  a  half  to 
two  hours)  the  pyloric  sphincter  relaxes  at  intervals  to  allow 
the  liquefied  food  to  pass  on  in  successive  portions  into  the 
duodenum.  At  the  end  of  three  or  four  hours  the  stomach 
is  ordinarily  emptied,  as  the  pyloric  sphincter  finally  relaxes 
to  such  an  extent  as  to  allow  even  the  large  indigestible 
masses  to  be  squeezed  into  the  intestines.* 

The  Chyle. — The  pancreas  commences  to  secrete  as  soon 

*  Several  of  the  above  facts  were  first  observed  on  a  Canadian  trapper, 
Alexis  St.  Martin,  who  as  a  result  of  a  gunshot  wound  had  a  permanent 
opening  from  the  surface  of  the  abdomen  to  the  interior  of  the  stomach. 


THE  PANCREATIC  SECRETION.  137 

as  food  enters  the  stomach  ;  hence  a  quantity  of  its  secretion 
is  already  accumulated  in  the  intestine  when  the  chyme  enters. 
The  gall-bladder  is  distended  with  bile,  secreted  since  the 
last  meal.  The  acid  chyme  stimulating  the  duodenal  mucous 
membrane  causes  a  reflex  contraction  of  the  muscular  coat  of 
the  gall-bladder,  and  a  gush  of  bile  is  poured  out  into  the 
chyme.  From  this  time  on  both  liver  aud  pancreas  continue 
secreting  actively  for  some  hours,  and  pour  their  products 
into  the  intestine.  The  glands  of  the  intestine  are  also  set  at 
work.  All  of  these  secretions  are  alkaline,  and  they  suffice 
very  soon  to  more  than  neutralize  the  acidity  of  the  gastric 
juice,  and  so  to  convert  the  acid  chyme  into  alkaline  chyle. 
This,  as  found  in  the  intestine  after  an  ordinary  meal,  con- 
tains water,  partly  swallowed  and  partly  derived  from  the 
salivary  and  other  secretions,  undigested  proteids,  some  un- 
changed starch,  oils  from  the  fats  eaten,  peptones  formed  in 
the  stomach  but  not  yet  absorbed,  salines  and  sugar,  which 
have  also  escaped  complete  absorption  in  the  stomach,  indi- 
gestible substances  taken  with  the  food,  together  with  the 
secretions  of  the  alimentary  canal. 

The  Pancreatic  Secretion  is  clear,  watery,  alkaline,  and 
much  like  saliva  in  appearance.  The  Germans  call  the  pan- 
creas the  "abdominal  salivary  gland."  In  digestive  prop- 
erties, however,  the  pancreatic  secretion  is  far  more  impor- 
tant than  the  saliva,  acting  not  only  on  starch  but  on  proteids 
and  fats.  On  starch  it  acts  like  the  saliva,  but  more  ener- 
getically because  of  the  presence  of  the  ferment  amylopsin. 
It  produces  changes  in  proteids  similar  to  those  effected  in 
the  stomach,  but  by  the  agency  of  the  ferment,  trypsin,  which 
differs  from  pepsin  in  being  able  to  act  in  an  alkaline,  neutral 
or  slightly  acid  solution.  Upon  fats  the  pancreatic  juice 
has  a  complex  effect.  Through  the  action  of  another  fer- 


138  THE  HUMAN  BODY. 

ment,  s/eapsm,  it  splits  up  a  portion  of  the  fats  into  fatty  acids 
and  glycerin.  The  alkali  present  unites  with  the  fatty  acids 
to  form  soap  in  sufficient  quantity  to  assist  in  emulsifying 
such  portion  of  the  fats  as  has  not  been  split  up.  This  pro- 
cess of  changing  fats  into  soaps  is  known  as  saponification. 
As  soap  and  glycerin  are  soluble  in  water  they  are  capable  of 
absorption.*  The  greater  part  of  the  fats  is  not,  however,  so 
broken  up,  but  merely  mechanically  separated  into  droplets 
which  remain  suspended  in  the  chyle  and  give  it  a  whitish 
color,  just  as  cream  particles  are  suspended  in  milk,  or  olive 
oil  in  mayonnaise  sauce.  If  oil  is  shaken  up  with  water,  the 
two  will  not  mix,  but  if  some  raw  egg  is  added  a  creamy 
mixture  is  readily  formed  in  which  the  oil  remains  for  a  long 
time  evenly  suspended  in  the  watery  menstruum.  The  rea- 
son of  this  is  that  each  oil  droplet  becomes  surrounded  by  a 
delicate  pellicle  of  albumen  and  is  thus  prevented  from  fusing 
with  its  neighbors  to  make  large  drops  which  would  soon 
float  to  the  top.  Such  a  mixture  is  called  an  emulsion,  and 
the  albumen  of  the  pancreatic  secretion  emulsifies  the  oils  in 
the  chyle,  making  it  white  because  the  innumerable  tiny  oil- 
drops  floating  in  it  reflect  all  the  light  which  falls  on  its  sur- 
face. It  is  probable  that  fats  in  this  condition  of  fine  divi- 
sion may  be  absorbed  without  further  change. 

The  saponification  of  fat,  like  the  peptonizing  of  proteids, 
is  but  a  step  in  the  process  of  getting  the  fat  into  the  blood. 
Fat  alone  is  found  in  the  blood  ;  hence  the  soap  formed  is 


I  Stearin        -}-  3  Water  =     3  Stearic  acid    -)-  I  Glycerin. 
Ordinary  soap  is  a  compound  of  a  fatty  acid  with   soda,  colored  and 
scented  by  the  addition  of  various  substances.     Soft  soap  is  a  compound 
of  a  fatty  acid  with  potash.    Both  dissolve  in  water,  though  the  fats  from 
which  they  are  made  will  not. 


THE  BILE.  139 

undoubtedly  reconverted  into  fat  by  the  union  of  the  fatty 
acids  and  glycerin. 

The  Bile. — Human  bile  when  quite  fresh  is  an  alkaline 
golden-brown  liquid.  It  contains  coloring  matters  derived 
from  broken-down  red  blood  corpuscles,  mineral  salts,  water, 
and  the  sodium  salts  of  two  nitrogenized  acids,  taurocholic 
and  gfycocholic,  of  which  the  former  predominates. 

The  Uses  of  Bile. — Bile  has  no  digestive  action  upon 
starch  or  proteids  and  does  not  break  up  fats.  Whether  it 
emulsifies  fats  has  been  a  matter  of  much  discussion.  It  has 
been  found  by  experimentation  that  if  a  rabbit  is  killed  after 
having  been  fed  with  oil,  no  milky  chyle  is  found  above  the 
point  where  the  pancreatic  duct  opens  into  the  intestine, 
although  the  bile  entered  and  mixed  with  the  intestinal  con- 
tents a  foot  above  this  opening.  The  bile  alone  does  not, 
therefore,  emulsify  fats  in  the  rabbit.  In  many  animals,  as 
in  man,  the  bile  and  pancreatic  ducts  open  together  into  the 
duodenum,  so  that  if  an  animal  is  killed  during  digestion  and 
emulsified  fats  are  found  in  the  chyle,  it  is  impossible  to  say 
whether  or  not  the  bile  had  a  share  in  the  process  of  emulsi- 
fication.  As,  however,  the  bile  of  rabbits  is  much  the  same 
as  that  of  other  animals,  it  has  been  inferred  that  the  bile 
does  not  emulsify  fats  in  the  intestine.  Some  have  even 
gone  so  far  as  to  say  that  the  inertness  of  bile  with  respect  to 
other  foodstuffs  makes  it  probable  that  it  has  no  digestive 
power  at  all,  but  is  merely  an  excretion  which  is  passed  out 
of  the  body  through  the  alimentary  canal. 

There  are  many  facts,  however,  which  militate  against  this 
view.  The  bile  enters  the  upper  end  of  the  small  intestine 
at  a  point  which  necessitates  its  traversing  more  than  twenty 
feet  before  it  can  pass  from  the  body.  Moreover,  a  large 
part  of  the  bile  is  reabsorbed  from  the  intestinal  tract,  to  be 


140  THE  HUMAN  BODY. 

again  secreted  by  the  liver  and  again  reabsorbed.  Thus 
there  is  a  strong  supposition  in  favor  of  its  being  intended 
for  special  use  in  the  intestinal  tract.  By  its  alkalinity  it 
undoubtedly  assists  in  overcoming  the  acidity  of  the  chyme 
and  so  allows  the  pancreatic  secretion  to  act  more  strongly. 
It  probably  helps  to  excite  the  contractions  of  the  muscular 
coats  of  the  intestines,  since  constipation  often  results  when 
the  bile  duct  is  temporarily  clogged,  as  it  usually  is  in  jaun- 
dice. It  probably  also  acts  as  a  preservative,  for  a  deficiency 
of  bile  secretion  is  said  to  lead  to  putrefaction  of  the  intes- 
tinal contents. 

There  are  other  facts,  moreover,  that  point  to  the  direct 
influence  of  the  bile  in  promoting  the  absorption  of  fats. 
If  one  end  of  a  very  narrow  glass  tube  is  moistened  with 
water,  oil  will  rise  in  it  but  slightly ;  if  the  tube  is  moistened 
with  bile  instead  of  water,  the  oil  will  ascend  higher. 
Again,  oil  passes  through  a  membrane  kept  moist  with 
bile  under  a  much  lower  pressure  than  through  one  wet 
with  water.  Hence,  it  is  quite  possible  that  bile,  by  moist- 
ening the  cells  lining  the  intestines,  may  facilitate  the  pas- 
sage of  oily  substances  into  the  villi  and  thus  promote  the 
absorption  of  fats. 

Moreover,  experiment  has  shown  that  if  the  bile  is  pre- 
vented from  entering  the  intestine  of  a  dog  he  eats  much 
more  food  than  before,  and  that  a  great  proportion  of  the 
fatty  part  passes  out  of  the  alimentary  canal  unabsorbed. 
There  is  no  doubt,  therefore,  that  the  bile  somehow  aids  in 
the  absorption  of  fats. 

The  Intestinal  Juice  consists  of  the  mixed  secretions  oi 
the  crypts  of  Lieberklihn  and  other  glands  of  the  intestine. 
It  is  very  difficult  to  obtain  it  pure,  and  hence  its  digestive 
action  is  imperfectly  known.  It  is  alkaline  and  helps  to  over- 


INTESTINAL  DIGESTION.  141 

come  the  acidity  of  the  chyme  and  to  allow  the  trypsin  of  the 
pancreas  to  act  on  proteids.  It  seems  capable  itself  of  dis- 
solving some  kinds  of  proteids  and  turning  them  into  pep- 
tones. 

Intestinal  Digestion. — Having  considered  separately  the 
digestive  actions  of  the  different  secretions  poured  into  the 
small  intestine,  we  may  now  consider  their  combined  action. 
The  acid  chyme  entering  the  duodenum  from  the  stomach  is 
more  than  neutralized  by  the  alkaline  secretions  which  it 
meets  in  the  small  intestine  ;  it  is  made  alkaline.  This  alka- 
linity allows  the  pancreatic  secretion  to  finish  the  solution 
and  transformation  of  proteids  into  peptones.  The  pancreatic 
secretion  also  continues  the  conversion  of  starch  into  maltose. 
The  bile  and  pancreatic  secretion  are  thoroughly  mixed  with 
the  fats  by  the  contractions  of  the  intestine,  producing  an 
emulsion,  which  is  taken  up  by  the  cells  lining  the  intestine. 
To  a  certain  extent  the  fats  are  also  saponified.  The  result 
of  all  these  processes  is  a  thin,  milky  alkaline  liquid  called 
chyle. 

Indigestible  Substances. — With  every  meal  several  things 
are  eaten  which  are  not  digestible.  Among  them  are  elastic 
tissue,  forming  a  part  of  the  connective  tissue  of  all  animal 
foods,  and  cellulose,  the  chief  constituent  of  the  cell  walls  in 
plants.  The  mucus  secreted  by  the  membrane  lining  the 
alimentary  tract  also  contains  an  indigestible  substance, 
mucin.  These  three  materials,  together  with  water,  un- 
digested foodstuffs,  the  coloring  matter  of  bile,  and  other 
excretory  substances  found  in  the  various  secretions  poured 
into  the  alimentary  canal,  form  a  residue  which  collects  in 
the  lower  end  of  the  large  intestine,  and  is  from  time  to  time 
expelled  from  the  rectum. 

The  regular  daily  expulsion  of  waste  matters  is  of  the  ut- 


142  THE  HUMAN  BODY. 

most  importance  from  the  standpoint  of  health.  If  the  food 
contains  too  little  indigestible  material  there  is  not  sufficient 
bulk  remaining  in  the  large  intestine  to  insure  its  being 
moved  forward  by  peristaltic  action  to  the  rectum  for  expul- 
sion. The  waste  matters  of  some  foods,  as  the  bran  of 
wheat,  the  fine  beard  of  oats,  by  their  irritation  of  the  intes- 
tinal wall  lead  to  a  more  vigorous  peristalsis.  Infrequent 
evacuation  permits  decomposition  through  the  activity  of  the 
hordes  of  bacteria  which  infest  the  large  intestine.  To  the 
absorption  of  the  products  of  decomposition  from  the  intes- 
tine are  to  be  attributed  some  of  the  harmful  effects  of  this 
condition.  This  is  so  common  a  trouble  that  it  is  not  sur- 
prising that  patent  medicines  owe  their  success  to  the  fact 
that  they  are  chiefly  laxative  and  thus  give  temporary  relief. 
Exercise,  regularity  of  habit,  the  use  of  foods  with  a  large 
share  of  waste,  such  as  bread  made  of  graham  flour,  onions, 
corn,  green  peas,  fruits,  and  the  drinking  of  plenty  of  water, 
are  the  best  preventives. 

Dyspepsia  is  the  common  name  of  a  variety  of  diseased 
conditions  attended  with  loss  of  appetite  or  troublesome 
digestion.  The  immediate  cause  of  the  symptoms  and  the 
treatment  necessary  may  vary  widely ;  the  detection  of  the 
cause  and  the  choice  of  the  proper  remedial  agents  often  call 
for  more  than  ordinary  medical  skill.  A  few  of  the  more 
common  forms  of  dyspepsia  may  be  mentioned  here,  with 
their  proximate  causes,  not  in  order  to  enable  people  to 
undertake  the  rash  experiment  of  dosing  themselves,  but  to 
show  how  wide  a  chance  there  is  for  any  unskilled  treatment 
to  miss  its  end  and  do  more  harm  than  good. 

Appetite  is  primarily  due  to  a  condition  of  the  mucous 
membrane  of  the  stomach,  which  in  health  comes  on  after  a 
short  fast  and  stimulates  its  sensory  nerves ;  loss  of  appetite 


ABSORPTION  FROM   THE  ALIMENTARY  CANAL.     143 

may  be  due  to  any  of  several  causes.  The  stomach  may  be 
apathetic  and  lack  its  normal  sensibility  so  that  the  empty  con- 
dition does  not  act  as  a  sufficient  excitant.  If  food  is  taken 
at  such  a  time  it  is  often  a  sufficient  stimulus,  and  "appetite 
comes  with  eating."  A  bitter  solution  before  a  meal  is  useful 
as  an  appetizer  to  patients  of  this  sort.  .On  the  other  hand, 
the  stomach  may  be  too  sensitive,  and  a  voracious  appetite 
be  replaced  by  nausea,  or  even  vomiting,  as  soon  as  a  few 
mouthfuls  have  been  swallowed ;  the  extra  stimulus  of  the 
food  overstimulates  the  too  irritable  stomach,  just  as  a 
draught  of  mustard  and  warm  water  overstimulates  a  healthy 
one.  The  proper  treatment  in  such  cases  should  be  sooth- 
ing.* In  states  of  general  debility,  when  the  stomach  is  too 
feeble  to  secrete  under  any  stimulation,  the  administration  of 
weak  acids  and  artificially  prepared  pepsin  is  needed  to  supply 
gastric  juice  until  the  improved  digestion  enables  the  stomach 
to  do  its  own  work. 

Enough  has  probably  been  said  to  show  that  dyspepsia  is 
not  a  disease,  but  a  symptom  accompanying  many  diseased 
conditions,  which  require  special  knowledge  for  their  treat- 
ment. Since  it  deprives  the  body  of  its  proper  nourishment, 
it  tends  to  intensify  itself  and  should  never  be  neglected. 

Absorption  from  the  Alimentary  Canal. — Through  its 
whole  extent  the  mucous  membrane  lining  the  digestive  tube 


*  When  food  is  taken  it  ought  to  stimulate  the  sensory  gastric  nerves, 
so  as  to  excite  the  reflex  centres  for  the  secretory  nerves  and  for  the  dila- 
tation of  the  blood  vessels  of  the  organ  ;  if  it  does  not,  the  gastric  juice  will 
be  imperfectly  secreted.  In  such  cases  one  may  stimulate  the  secretory 
nerves  by  weak  alkalies  (p.  133),  as  apollinaris  water  or  a  little  carbonate 
of  soda,  before  meals  ;  or  give  drugs,  as  strychnine,  which  increase  the 
irritability  of  reflex  nerve  centres.  The  vascular  dilatation  may  be  helped 
by  warm  drinks,  and  this  is  probably  the  rationale  of  the  glass  of  hot 
water  after  eating  which  has  been  in  vogue. 


J44  THE  HUMAN  BODY. 

is  traversed  by  a  very  close  meshwork  of  blood  and  lymph 
vessels.  Matters  ready  for  absorption  pass  through  or  be- 
tween the  cells  covering  the  surface  of  the  mucous  membrane 
and  then  through  the  very  thin  walls  of  the  smallest  blood 
and  lymph  vessels  ;  by  these  they  are  conveyed  to  the  larger 
channels  leading  to  the  heart.  From  the  heart  the  digested 
and  absorbed  food  is  distributed  to  every  part  of  the  body. 

Absorption  from  the  Mouth,  Pharynx,  and  Gullet  is  ordi- 
narily slight.  Water,  common  salt,  sugar  and  grape  sugar 
are  no  doubt  taken  up  during  the  processes  of  chewing  and 
swallowing,  but  the  time  which  elapses  between  taking  a 
mouthful  of  food  and  its  transference  to  the  stomach  is  usually 
too  short  to  allow  any  considerable  absorption. 

Absorption  from  the  Stomach. — Food  stays  in  the  stomach 
a  considerable  time,  and  it  might  be  supposed  that  absorbable 
material  would  be  taken  up  to  a  considerable  extent  by  the  mu- 
cous membrane  of  the  stomach  and  passed  on  into  the  general 
blood  current.  As  a  matter  of  fact,  experiments  have  demon- 
strated very  little  absorption  in  this  way. 

Absorption  from  the  Small  Intestine  is  by  far  the  most 
important  in  bringing  nutritive  matters  into  the  body. 
The  stomach  is  an  organ  rather  of  digestion  than  absorption  ; 
the  small  intestine,  on  the  other  hand,  is  specially  constructed 
to  absorb.  Its  valvulae  conniventes  delay  the  progress  of  the 
food  mass,  while  its  innumerable  villi,  with  their  blood  vessels 
and  lymphatics  (p.  125),  reach  out,  like  so  many  rootlets, 
into  the  chyle  to  take  it  up. 

The  sugars  reaching  the  small  intestine  or  formed  in  it  are 
absorbed  mainly  into  the  blood  and  carried  to  the  liver, 
where  they  are  turned  into  glycogen  for  storage.  The  pep- 
tones passed  into  the  intestine  from  the  stomach,  or  formed 
in  it  by  the  action  of  the  pancreatic  secretion,  are  taken  up 


THE  LACTEALS-DIALYS1S.  H5 

both  by  the  lymphatics  and  by  the  blood  vessels.  The  emulsi- 
fied fats  pass  into  the  lymphatics  of  the  villi  and  are  carried 
by  them  to  the  blood. 

The  Lacteals. — The  innumerable  tiny  fat  drops  drained 
off  by  the  intestinal  lymphatics  or  lacteah  after  an  ordinary 
meal  make  their  contents  look  white  and  milky,  hence  the 
name.*  During  fasting  the  lymphatics  of  the  small  intestine, 
like  those  in  other  parts  of  the  body  (see  Chap.  XIII.)  con- 
vey a  clear  colorless  liquid. 

Dialysis. — When  two  specimens  of  water  containing  differ- 
ent matters  in  solution  are  separated  from  one  another  by  a  moist 
animal  membrane,  an  interchange  of 
material  will  take  place  under  certain 
conditions.  If  a  solution  of  common 
salt  is  placed  in  an  apparatus  (Fig.  66) 
on  one  side  (-#)  of  an  animal  mem- 
brane, and  a  solution  of  sugar  in  water 
on  the  other  side  (C),  it  will  be  found 
after  a  time  that  some  salt  has  got  into 

tic.  66. — Dialyzing  apparatus. 

Cand  some  sugar  into  B,  although  there  £  «S£Sg^^ 
are  no  visible  pores  in  the  partition,  ^k  in  tube'  c'su^ar  in 
and  the  pressure  of  the  liquid  is  the 

same  on  both  sides,  Such  an  interchange  is  said  to  be  due  to 
dialysis  or  osmosis,  and  if  the  process  is  allowed  to  go  on  for 
some  hours  the  same  proportions  of  salt  and  sugar  will  be 
found  in  the  solutions  on  each  side  of  the  dividing  membrane. 
Substances  differ  much  in  the  rapidity  with  which  they  may 
be  dialyzed.  Salts  of  various  kinds  ordinarily  dialyze  much 
more  rapidly  than  sugar,  peptone,  etc.  Many  substances  are 
incapable  of  dialyzation.  Food  materials  are  almost  univer- 
sally found  among  these,  and  hence  there  is  the  necessity 

*  From  Latin  lac,  milk. 


1 46  THE  HUMAN  BODY. 

for  digestion,  which,  by  making  the  foods  dialyzable,  facili- 
tates their  absorption.  Substances  which  are  dialyzable  are 
called  crystalloids,  those  which  are  not,  colloids. 

Absorption  from  the  Large  Intestine. — In  the  duodenum 
the  bulk  of  food  entering  from  the  stomach  is  increased  by 
the  bile  and  pancreatic  secretions.  Thenceforth  absorption 
overbalances  secretion,  and  the  food  mass  becomes  less  and 
less  in  bulk  to  the  lower  end  of  the  ileum.  The  contractions 
of  the  small  intestine  push  forward  its  continually  diminishing 
contents,  until  they  reach  the  ileo-caecal  valve,  through  which 
they  are  ultimately  pressed.  When  the  mass  enters  the  large 
intestine  its  nutritive  portions  have  been  almost  entirely  ab- 
sorbed, and  it  consists  chiefly  of  water,  with  the  indigestible 
portions  of  the  food  and  the  secretions  of  the  alimentary 
canal.  It  contains  cellulose,  elastic  tissue,  mucus,  altered  bile 
pigments,  fat  if  a  large  quantity  has  been  eaten,  and  starch 
if  raw  vegetables  have  formed  part  of  the  diet. 

In  the  large  intestine  there  is  a  considerable  absorption  of 
water  and  of  the  unabsorbed  products  of  digestion.  It  is 
probable  that  digestion  may  continue  to  some  degree  here. 
When  artificially  prepared  foods  are  injected  into  the  rectum 
in  sufficient  amounts,  the  absorption  is  rapid  enough  to  sus- 
tain life  for  several  weeks  under  favorable  conditions,  although 
no  food  is  taken  into  the  stomach. 

Finally  the  residue  is  expelled  from  the  body. 


CHAPTER   XIII. 
BLOOD  AND  LYMPH. 

Why  We  Need  Blood. — Some  very  small  animals  of  simple 
structure  require  no  blood  ;  every  part  catches  its  own  food 
and  gives  off  its  own  wastes  to  the  air  or  water  in  which  the 
creature  lives.  •  When,  however,  an  animal  is  larger  and 
made  up  of  many  organs,  some  of  which  are  far  away  from  the 
surface  of  its  body,  this  is  impossible  ;  some  organs  are  there- 
fore set  apart  to  catch  food,  and  arrangements  made  to  carry 
this  food  to  the  others.  In  our  own  bodies  many  parts  lie  far 
away  from  the  stomach  and  intestines  which  receive,  digest, 
and  absorb  our  food,  and  from  the  lungs  which  take  oxygen 
from  the  air ;  yet  every  part,  bone  and  muscle,  brain  and 
nerve,  skin  and  gland,  needs  a  constant  supply  of  these 
to  keep  it  alive.  The  division  of  labor,  in  accordance  with 
which  some  organs  are  especially  set  apart  for  the  purpose  of 
receiving  substances  from  the  outside  world  to  minister  to  the 
growth  and  repair  of  the  body  and  to  furnish  energy,  necessi- 
tates an  arrangement  by  which  the  matters  received  shall  be 
distributed  to  other  parts.  The  distribution  is  accomplished 
by  the  blood,  which  goes  to  every  organ  from  the  crown  of  the 
head  to  the  sole  of  the  foot.  As  it  flows  from  part  to  part,  the 
blood  takes  nourishment  from  the  alimentary  tract  and  oxygen 
from  the  lungs,  and  gives  them  out  to  the  parts  which  need 
them. 


148  THE  HUMAN  BODY. 

The  Removal  of  Wastes. — The  rapidly  flowing  blood  not 
only  conveys  a  supply  of  nutritive  material  for  all  the  organs, 
but  is  a  sort  of  sewage  stream  that  drains  off  their  wastes 
(p.  86),  and  carries  them  to  the  excretory  organs,  by  which 
they  are  removed  from  the  body. 

The  blood  is  a  middleman,  trading  between  the  receiving 
organs  (lungs  and  alimentary  canal)  and  the  tissues  of  the 
body,  and  again  between  the  tissues  and  the  excretory  organs. 
Each  part  is  thus  kept  supplied  with  food  and  freed  from 
wastes,  though  it  may  lie  far  distant  from  all  places  where 
new  materials  first  enter  the  body,  and  from  those  where 
refuse  and  deleterious  substances  are  finally  passed  from  it. 

The  Blood,  as  every  one  knows,  is  a  red  liquid  which 
is  very  widely  distributed  over  the  body,  since  it  flows  from 
any  part  of  the  surface  when  the  skin  is  cut.  There  are,  how- 
ever, a  few  parts  into  which  blood  is  not  carried.  The  outer 
layer  of  the  skin,*  hairs  and  nails,  the  hard  parts  of  the  teeth 
and  most  cartilages  contain  no  blood  ;  these  non-vascular 
tissues  are  nourished  by  liquid  which  soaks  through  the  walls 
of  blood  vessels  in  neighboring  parts. 

The  Histology  of  Blood. — Fresh  blood  is  to  the  unassisted 
eye  a  red  opaque  liquid  showing  no  sign  of  being  made  up  of 
different  parts  ;  but  when  examined  by  a  microscope  it  is  seen 
to  consist  of  a  liquid,  the  blood  plasma,  which  has  floating  in  it 
countless  multitudes  of  closely  crowded  and  extremely  minute 
solid  bodies  known  as  blood  corpuscles.  The  plasma  is  color- 
less and  watery -looking  ;  the  corpuscles  are  of  two  kinds,  red 
and  colorless.  The  red  corpuscles  are  by  far  the  most  numer- 
ous and  give  the  blood  its  color ;  they  are  so  tiny  and  so 

*  The  absence  of  blood  in  the  superficial  layer  of  the  skin  may  be 
readily  shown  :  take  a  fine  needle  threaded  with  silk  ;  by  taking  shallow 
stitches  a  pattern  can  be  easily  embroidered  on  the  palm  or  back  of  the 
hand  without  drawing  a  drop  of  blood. 


TL 


PLATE  III.— A  GENERAL  VIEW  OF  THE  LYMPHATICS  OR  ABSORBENTS.       That  portion  of  them 
known  as  the  lacteals  is  seen  at  d,  passing  from  the  small  intestine  e  to  the  thoracic  duct  /. 


EXPLANATION  OF  PLATE  III. 

A    GENERAL  VIEW  OF  THE  LYMPHATIC  OR  ABSORBENT  SYSTEM 
OF  VESSELS. 

At  e  is  seen  a  portion  of  the  small  intestine  from  which  lacteals  or 
chyle-conveying  vessels,  d,  proceed  (their  origin  within  the  villi  may  be 
seen  magnified  in  fig.  61)  ;  at/" the  thoracic  duct,  into  which  the  lacteals 
open.  This  duct  passes  up  the  back  of  the  chest,  and  opens  into  the 
great  vein  at  g,  on  the  left  side  of  the  neck  :  here  the  chyle  mingles  with 
the  venous  blood.  In  the  right  upper  and  lower  limbs  the  superficial 
lymphatic  vessels  1 1 1 1,  which  lie  beneath  the  skin,  are  represented.  In 
the  left  upper  and  lower  limbs  the  deep  lymphatic  vessels  which  accom- 
pany the  deep  blood  vessels  are  shown.  The  lymphatic  vessels  of  the 
lower  limbs  join  the  thoracic  duct  at  the  spot  where  the  lacteals  open  into 
it :  those  from  the  left  upper  limb  and  from  the  left  side  of  the  head  and 
neck  open  into  that  duct  at  the  root  of  the  neck.  The  lymphatics  from 
the  right  upper  limb  and  from  the  right  side  of  the  head  and  neck  join 
the  great  veins  at  n.  At  m  m  are  seen  the  enlargements  called  lymphatic 
glands,  situated  in  the  course  of  the  lymphatic  vessels.  These  vessels 
convey  a  fluid  called  lymph,  which  mingles  with  the  blood  in  the  great 
veins.  A  fuller  account  of  the  lymphatic  vessels  in  general,  as  distin- 
guished from  that  section  of  them  known  as  the  lacteaL,  will  be  found  on 
P-  159- 


RED  BLOOD  CORPUSCLES. 


149 


plentiful  that  about  five  millions  of  them  are  contained  in 
a  drop  of  blood  the  size  of  a  small  pinhead  (i  cu.  mm.). 
They  are  so  closely  packed  that  the  unaided  eye  cannot  see 


FIG.  67. — Blood  corpuscles.  A,  magnified  about  400  diameters.  The  red  cor- 
puscles have  arranged  themselves  in  rouleaux;  a.  a,  colorless  corpuscles;  £,  red 
corpuscles  more  magnified  and  seen  in  focus  ;  J5,  a  red  corpuscle  slightly  out  of  focus. 
Near  the  right-hand  top  corner  is  a  red  corpuscle  seen  in  three-quarter  face,  and  at  C 
one  seen  edgewise,  f,  G,  H,  /,  white  corpuscles  .highly  magnified. 

the  spaces  between  them,  and  so  the  whole  blood  appears 
uniformly  red. 

Red  Blood  Corpuscles. — The  red  corpuscles  of  human 
blood  (Fig.  67)  are  circular  disks  slightly  hollowed  out  on 
each  face.  Seen  .singly  with  a  microscope  each  is  not 
red  but  pale  yellow  ;  a  drop  of  blood  spread  out  very  thin  on 
glass,  or  mixed  with  a  tablespoonftil  of  water,  is  also  pale 
yellow  ;  the  corpuscles  look  red  only  when  they  are  crowded 
together  in  a  mass.  Soon  after  blood  is  drawn  most  of  the 
red  corpuscles  cohere  side  by  side  in  rows,  something  like 
piles  of  coin. 


THE  HUMAN  BODY. 

The  red  corpuscles  of  most  mammalia  resemble  those  of 

man  in  being  circular  bi- 
concave pale  yellow  disks; 
those  of  camels  and  drom- 
edaries, however,  are  oval. 
The  red  blood  corpuscles 
of  birds,  reptiles,  amphib- 

Fxo.68.-Red  corpuscles  of  the  frog.  .^    ^   fishes    ^    ^ 

and  contain  a  nucleus  in  the  centre  such  as  is  not  found  in 
human  red  corpuscles. 

The  Origin  of  the  Red  Corpuscles. — In  adult  life  the  red 
blood  corpuscles  are  constantly  being  destroyed  and  as  con- 
stantly renewed.  They  are  developed  in  the  red  marrow  of 
the  bones,  thrown  into  the  blood  current  to  perform  their 
work  of  carrying  oxygen,  and  when  apparently  no  longer 
able  to  do  this  work  successfully,  are  destroyed  by  the 
liver. 

Haemoglobin. — Each  red  corpuscle  is  soft  and  jelly-like. 
Its  chief  constituent,  besides  water,  is  a  proteid  substance 
containing  iron,  h&m' o-glo-bin,  which  has  the  power  of  com- 
bining with  oxygen  when  in  a  place  where  oxygen  is  plenti- 
ful, and  of  giving  it  off  again  in  a  region  where  it  is  present 
in  small  amount  or  not  at  all.  This  enables  the  blood  to  carry 
oxygen  from  the  lungs  to  the  active  tissues  which  have  used 
up  their  supply. 

Haemoglobin  itself  is  dark  purplish-red  in  color ;  haemo- 
globin combined  with  oxygen  is  bright  scarlet.  Accordingly, 
the  blood  which  flows  to  the  lungs  after  giving  up  its  oxygen 
is  dark  red,  but  becomes  a  bright  scarlet  after  having  received 
a  fresh  supply  of  oxygen  from  them. 

The  Colorless  Blood  Corpuscles  are  a  little  larger  than  the 
red,  but  much  less  numerous  (about  i  to  300).  As  their 


THE  COLORLESS  BLOOD  CORPUSCLES.  IS1 

name  implies,  they  contain  no  coloring  matter.  Each  is  a 
cell  with  a  nucleus,  and  has  the  won- 
derful power  of  changing  its  shape. 
Watched  with  a  microscope  the  cor- 
puscles may  be  seen  to  alter  their 
form  slowly  (Fig.  69),  or  even  to 
creep  across  the  glass.  Their  move- 
ments are  very  like  those  of  the  micro- 
scopic  animal  named  amvba,  and  are 

,.        ,  n     j  z     -j         TO,  form    due     to     its     amoeboid 

accordingly  called  amceboid.  Ihese  movements. 
corpuscles  are  thus  little,  independently  moving  cells  which 
live  in  the  liquid  of  the  blood.  They  apparently  have  the 
power  of  taking  into  their  substance  any  foreign  particles  such 
as  broken-down  cells,  bits  of  pigment  which  have  been  in- 
jected to  test  their  voracity,  and  bacteria.  These  particles 
they  digest  by  a  chemical  process  not  unlike  in  its  results  that 
which  takes  place  in  the  alimentary  tract  of  higher  animals. 
They  have  the  power  of  passing  through  the  walls  of  the  cap- 
illaries and  of  wandering  about  through  the  tissues  of  the 
body,  literally  "  seeking  what  they  may  devour."  Doubtless 
many  disease-producing  bacteria  which  have  entered  the  body 
either  through  the  lungs  or  by  way  of  the  mouth  are  success- 
fully destroyed  by  the  white  blood  corpuscles.  This  process 
is  called  phagocytosis. 

It  is  claimed  by  some  that  the  main  explanation  of  the 
body's  resistance  to  many  kinds  of  infection  (invasion  by 
bacteria)  is  found  in  the  protection  thus  afforded  by  white 
blood  corpuscles,  and  that  the  strength  of  the  resistance  is  in 
proportion  to  the  vigor  of  the  corpuscles.  When  the  bacte- 
rial invasion  is  too  great  to  be  handled  successfully,  the  cor- 
puscles are  themselves  destroyed  by  the  bacteria.  In  abscesses 
we  have  usually  a  battleground  of  these  two  forces.  The  in- 


THE  HUMAN  BODY 

vasion  of  the  bacteria  through  a  scratch  or  cut  leads  to  irrita- 
tion of  the  tissues ;  this  in  turn  leads  to  the  advance  of  the 
army  of  corpuscles.  In  the  struggle  many  of  the  combatants 
on  both  sides  are  destroyed.  Many  times  the  corpuscles 
collect  in  such  numbers  that  they  fill  up  the  tissues  and  even 
clog  the  circulation  of  the  blood,  thus  shutting  off  food  from 
themselves  and  the  tissues  and  contributing  to  their  own  de- 
feat. In  the  discharge  (pus)  from  such  abscesses,  white 
blood  corpuscles  are  found  in  immense  numbers. 

The  Coagulation  of  Blood. — When  blood  is  first  drawn 
from  the  living  body  it  is  perfectly  liquid,  flowing  as  readily 
as  water.  This  condition  is  only  temporary  ;  in  a  few  min- 
utes the  blood  becomes  sticky  and  resembles  a  thick  red  syrup; 
the  thickening  becomes  more  and  more  marked,  until,  after 
the  lapse  of  five  or  six  minutes,  the  whole  mass  is  a  firm  jelly 
and  adheres  to  the  vessel  containing  it,  so  that  this  may  be 
inverted  without  spilling.  This  stage  is  known  as  that  of 
gelatinization,  and  is  also  not  permanent.  In  a  few  minutes 
the  top  of  the  jelly-like  mass  will  be  seen  to  be  hollowed  or 
"  cupped,"  and  in  the  concavity  will  be  found  a  small  quan- 
tity of  nearly  colorless  liquid,  the  blood  serum.  The  jelly 
next  shrinks  so  as  to  pull  itself  loose  from  the  sides  and  bot- 
tom of  the  vessel  containing  it,  and  as  it  shrinks  it  squeezes  out 
more  and  more  serum.  Ultimately  we  get  a  solid  clot,  colored 
red  and  smaller  in  size  than  the  vessel  in  which  the  blood  co- 
agulated, but  retaining  its  form,  and  floating  in  a  quantity  of 
pale  yellow  serum.  The  whole  series  of  changes  leading  to 
this  result  is  known  as  the  coagulation  or  clotting  of  the  blood. 

Cause  of  Coagulation. — If  a  drop  of  freshly  drawn  blood 
is  studied  under  the  microscope,  one  will  observe  beside  the 
red  and  white  blood  corpuscles  a  colorless  liquid  in  which 
they  float.  This  is  the  plasma  of  the  blood.  Very  fine  solid 


DEFIBRINATED  OR   WHIPPED  BLOOD.  153 

threads  will  be  seen  to  separate  out  from  the  blood.  These 
quickly  run  through  the  plasma  in  every  direction  and  form  a 
close  network  entangling  the  corpuscles.  These  threads  are 
composed  of  an  albuminous  (proteid)  substance  known  as 
fibrin.  When  they  first  form,  the  whole  drop  is  much  like  a 
sponge  soaked  full  of  water  (represented  by  the  serum),  and 
having  solid  bodies  (the  corpuscles)  caught  in  its  meshes. 
After  the  fibrin  threads  have  been  formed  they  begin  to 
shorten;  hence  the  fibrinous  network  tends  to  shrink  in  every 
direction,  and  this  shrinkage  is  greater  the  longer  the  clotted 
blood  is  kept.  At  first  the  threads  stick  too  firmly  to  the 
bottom  and  sides  of  the  vessel  to  be  pulled  away,  and  thus 
the  first  sign  of  the  contraction  of  the  fibrin  is  seen  in  the 
cupping  of  the  surface  of  the  gelatinized  blood  where  the 
threads  have  no  solid  attachment,  and  there  the  contracting 
mass  presses  out  from  its  meshes  the  first  drops  of  serum. 
Finally  the  contraction  of  the  fibrin  overcomes  its  adhesion  to 
the  vessel,  and  the  clot  pulls  itself  loose  on  all  sides,  pressing 
out  more  and  more  serum.  The  great  majority  of  the  red 
corpuscles  are  held  back  in  the  meshes  of  the  fibrin. 

The  clotting  of  blood  takes  place  only  when  blood  is  out- 
side of  the  body,  and  is  due  to  the  action  of  a  ferment  (fibrin- 
fermenf}  upon  one  of  the  proteid  substances  dissolved  in  the 
plasma  (fibrinogen).  This  coagulation  of  the  blood  resembles 
closely  that  of  muscle,  which  is  also  caused  by  the  action  of  a 
ferment.  The  total  amount  of  fibrin  formed  is  slight  (o.2# 
of  the  weight  of  the  blood). 

Defibrinated  or  Whipped  Blood. — As  the  essential  point 
in  coagulation  is  the  formation  of  fibrin  in  the  plasma,  and  as 
blood  only  forms  a  certain  amount  of  fibrin,*  if  this  is  re- 

*  Fibrin  is  formed  from  fibrinogen,  a  soluble  albumen  existing  in  blood 
plasma. 


154  THE  HUMAN  BODY. 

moved  as  fast  as  it  forms  the  remaining  blood  will  not  clot. 
The  fibrin  may  be  separated  by  what  is  known  as  "whipping  " 
the  blood.  For  this  purpose  freshly  drawn  blood  is  stirred 
vigorously  with  a  bunch  of  twigs,  to  which  the  sticky  fibrin 
threads  adhere  as  they  form.  If  the  twigs  are  withdrawn  a 
quantity  of  stringy  material  will  be  found  attached  to  them. 
This  is  at  first  colored  red  by  adhering  blood  corpuscles,  but 
if  washed  in  water  pure  white  fibrin  may  tye  obtained  in  the 
form  of  highly  elastic  threads.  The  blood  from  which  the 
fibrin  has  been  removed  looks  like  ordinary  blood,  but  has 
lost  its  power  of  coagulating  spontaneously. 

Uses  of  Coagulation. — The  living  circulating  blood  in  the 
healthy  blood  vessels  does  not  clot,  because  it  contains  no 
solid  fibrin,  but  this  forms  in  it  when  the  blood  gets  out  of 
the  heart  or  blood  vessels,  or  when  the  lining  of  these  is  in- 
jured. In  a  wound,  the  clots  close  up  the  mouths  of  the  small 
vessels  which  have  been  opened  and  stop  the  bleeding,  which 
might  otherwise  go  on  indefinitely.  So,  too,  when  a  surgeon 
ties  an  artery,  the  tight  ligature  crushes  or  tears  its  delicate 
inner  surface,  and  causes  the  blood  to  clot  there.  The  clot 
becomes  more  and  more  solid,  and  by  the  time  the  ligature  is 
removed  is  organized  into  a  firm  plug  which  effectually  closes 
the  artery. 

The  Composition  of  Blood  Serum. — About  one  half  of  the 
bulk  of  fresh  blood  is  corpuscles  and  the  other  half  plasma 
minus  the  constituents  of  fibrin.  What  the  plasma  contains 
we  may  learn  by  examining  blood  serum,  which  is  plasma 
minus  fibrinogen. 

Blood  serum  is  very  different  from  water  ;  if  we  keep  0,1 
boiling  pure  water  in  a  saucepan  it  will  all  go  off  in  steam  and 
leave  nothing  behind,  but  if  we  try  to  boil  serum  we  find  that 
we  cannot  do  it ;  before  it  gets  as  hot  as  boiling  water  it  sets 


THE  BLOOD  G4SES.  155 

into  a  stiff,  solid  mass  just  like  the  white  of  a  hard-boiled  egg. 
In  fact  the  serum  contains  dissolved  in  it  two  albumins  very 
like  that  in  the  white  of  an  egg,  and  coagulated  in  a  similar 
way  by  boiling.  About  eight  and  a  half  pounds  of  albuminous 
substances  exist  in  one  hundred  pounds  of  blood. 

Blood  serum  also  contains  considerable  quantities  of  oily 
and  fatty  matters,  a  little  sugar,  some  common  salt  and  car- 
bonate of  soda,  and  small  quantities  of  very  many  other 
things,  chiefly  waste  products  from  the  various  tissues.  Nine 
tenths  of  the  blood  plasma  is  water. 

Composition  of  the  Red  Corpuscles. — In  the  fresh  moist 
state  these  contain  a  little  more  than  half  their  weight  of 
water.  Nine  tenths  of  their  solid  part  is  haemoglobin,  of 
which  iron  is  one  of  the  constituents  ;  they  also  contain  salts 
of  phosphorus  and  of  potassium. 

The  Blood  Gases. — Ordinary  fresh  or  salt  water  has  a  good 
deal  of  air  dissolved  in  it ;  upon  this  fishes  depend  for  their 
oxygen.  Blood  also  contains  a  quantity  of  gases  which  it 
gives  off  when  exposed  to  a  vacuum,  about  sixty  pints  of  gas 
to  a  hundred  pints  of  blood.  These  gases  are,  chiefly,  oxygen 
and  carbon  dioxide.  In  the  lungs  the  carbon  dioxide  diffuses 
out  from  the  plasma  of  the  blood  in  which  it  is  dissolved  into 
the  air  contained  in  the  air  cells.  From  this  air  oxygen  dif- 
fuses into  the  blood,  to  be  taken  up  by  the  haemoglobin  of 
the  red  blood  corpuscles.  Hence  the  blood  coming  from  the 
lungs  is  richer  in  oxygen  and  poorer  in  carbon  dioxide.  In 
the  tissues  which  have  only  the  carbon  dioxide,  this  gas 
pushes  its  way  into  the  blood,  while  the  oxygen  of  the 
blood  goes  out  to  be  used  by  the  tissues;  hence  the  blood  re- 
turning to  the  heart  is  richer  in  carbon  dioxide  and  poorer  in 
oxygen. 

The  Blood  as  a  Medium  of  Exchange. — "  Blood,  then,  is  a 


IS6  THE  HUMAN  BODY. 

very  wonderful  fluid  :  wonderful  for  being  made  up  of  colored 
corpuscles  and  colorless  fluid,  wonderful  for  its  fibrin  and 
power  of  clotting,  wonderful  for  the  many  substances,  for  the 
proteids,  for  the  ashes  or  minerals,  for  the  rest  of  the  things 
which  are  locked  up  in  the  corpuscles  and  in  the  serum. 

"  But  you  will  not  wonder  at  it  when  you  come  to  see  that 
the  blood  is  the  great  circulating  market  of  the  body,  in 
which  all  the  things  that  are  wanted  by  all  parts,  by  the 
muscles,  by  the  brain,  by  the  skin,  by  the  lungs,  liver,  and 
kidneys,  are  bought  and  sold.  What  the  muscle  wants  it 
buys  from  the  blood  ;  what  it  has  done  with  it  sells  back  to 
the  blood ;  and  so  with  every  other  organ  and  part.  As  long 
as  life  lasts  this  buying  and  selling  is  forever  going  on,  and 
this  is  why  the  blood  is  forever  on  the  move,  sweeping  rest- 
lessly from  place  to  place,  bringing  to  each  part  the  things  it 
wants,  and  carrying  away  those  with  which  it  has  done. 
When  the  blood  ceases  to  move,  the  market  is  blocked,  the 
buying  and  selling  cease,  and  all  the  organs  die,  starved  for 
the  lack  of  the  things  which  they  want,  choked  by  the  abun- 
dance of  things  for  which  they  have  no  longer  any  need. ' ' 
Foster. 

Hygienic  Remarks. — The  blood  flowing  from  any  organ 
will  have  lost  or  gained,  or  both  gained  and  lost,  when  com- 
pared with  the  blood  which  entered  it.  But  the  losses  and 
gains  in  particular  parts  of  the  body  are  in  such  small  propor- 
tion, with  the  exception  of  the  blood  gases,  as  to  elude  analy- 
sis for  the  most  part ;  moreover,  since  the  blood  from  all 
parts  is  mixed  up  in  the  heart,  they  balance  one  another  and 
produce  a  tolerably  constant  average.  In  health,  however, 
the  red  corpuscles  are  present  in  greater  proportion  after 
a  meal  than  before.  Healthy  sleep  in  proper  amount  also 
increases  the  proportion  of  red  corpuscles,  while  want  of  it 


THE  LYMPH.  157 

diminishes  their  number,  as  may  be  recognized  in  the  pallid 
aspect  of  a  person  who  has  lost  several  nights'  rest.  Fresh  air 
favors  their  increase.  Ancemia  is  a  diseased  condition  char- 
acterized by  pallor  due  to  deficiency  of  red  blood  corpuscles, 
and  accompanied  by  languor  and  listlessness.  It  is  not  unfre- 
quent  in  young  girls  on  the  verge  of  womanhood,  and  in  per- 
sons overworked  and  confined  within  doors.  It  must  be  remem- 
bered that  the  oxygen-carrying  power  of  the  blood  is  usually 
reduced  in  even  greater  proportion  than  the  reduction  in  the 
number  of  red  corpuscles  would  indicate.  Since  thereby  the 
capacity  for  effort  is  correspondingly  reduced,  it  is  important 
for  anaemic  persons  to  take  only  moderate  exercise.  Fresh 
air  and  good  food  are  the  best  remedies  though  medicines 
containing  iron  are  often  of  great  use. 

The  Quantity  of  Blood  in  the  Body. — The  total  weight  of 
the  blood  is  about  one  thirteenth  that  of  the  whole  body  ;  a 
man  of  average  size  contains  about  twelve  pounds  of  blood. 

The  Lymph. — The  blood  lies  everywhere  in  closed  tubes, 
and  consequently  does  not  come  into  direct  contact  with  any 
of  the  body  cells,  except  those  which  float  in  it  and  those 
which  line  the  interior  of  the  blood  vessels.  At  two  points 
in  its  course  (the  capillaries  of  tissues  and  capillaries  of  lungs), 
however,  the  vessels  through  which  it  passes  have  extremely 
thin  walls,  which  permit  the  plasma  to  transude  and  bathe 
the  various  tissues.  The  transuded  plasma  is  called  lymph. 
It  oozes  through  the  walls  of  the  capillaries  into  the  spaces 
between  the  cells  of  the  tissues  and  thus  becomes  the  essential 
means  of  nourishing  the  cells  of  the  body. 

The  lymph  commonly  contains  all  the  elements  of  the  blood 
except  the  red  blood  corpuscles,  though  these  elements  are 
not  found,  upon  analysis,  to  be  in  the  same  proportions  as  in 
the  blood  itself. 


I58  THE  HUMAN  BODY. 

The  Renewal  of  the  Lymph. — The  lymph  present  in  any 
organ  both  gives  to  and  receives  from  the  cells ;  and  so,  al- 
though it  may  have  originally  been  like  the  plasma  of  the 
blood,  it  soon  acquires  a  different  chemical  composition. 
The  cells  take  from  it  food  materials  to  keep  up  their 
activity,  and  give  to  it  the  wastes  resulting  from  such  activity. 


FIG.  70. — Origin  of  lymphatics  (after  Landois).  S,  lymph  spaces  communicating 
with  lymphatic  vessel;  .-i,  origin  of  lymphatic  by  union  of  lymph  spaces;  £,  £, 
cndothelial  cells  forming  wall  of  lymph  vessel. 

Thus  the  lymph  becomes  progressively  poorer  in  the  essential 
constituents  of  the  plasma  and  richer  in  waste  matters.  The 
lymph  is  constantly  drained  out  of  the  intercellular  spaces 
into  the  well-defined  lymph  channels,  and  slowly  finds  its  way 
through  successive  bunches  of  lymph  glands  back  into  the 
blood.  Fresh  plasma  constantly  exudes  from  the  capillaries 
to  take  the  place  of  the  lymph  in  the  intercellular  spaces  and 


THE  LYMPHATIC  VESSELS  OR  ABSORBENTS.       i$9 

to  carry  fresh  food  to  the  cells,  again  to  be  drained  off 
through  the  lymphatic  circulation.  The  exchanges  of  oxygen 
and  carbon  dioxide  are  chiefly  by  diffusion  between  the  tissues 
and  the  blood,  and  do  not  depend  upon  the  lymph. 

The  total  amount  of  lymph  passing  back  again  into  the 
blood  circulation  has  been  estimated  to  be  equal  to  the  total 


FIG.  71. — Superficial  lymphatics  and  glands.     G.  Axillary  glands. 

bulk  of  the  blood,  that  is,  one  thirteenth  of  the  weight  of  the 
body. 

In  consequence  of  the  different  wants  and  wastes  of  various 
cells,  and  of  the  same  cells  at  different  times,  the  lymph  must 
vary  considerably  in  composition  in  various  organs  of  the 
body.  . 

The  Lymphatic  Vessels  or  Absorbents. — The  cells  of  the 
body,  except  the  compact  layers  of  epithelium  composing 
surfaces,  are  rather  loosely  arranged  in  the  various  tissues  and 


i6o 


THE  HUMAN  BODY. 


organs.     In  the  irregular  branching  spaces  between  the  cells, 
the  lymph  which  has  exuded  from  the   capillaries   finds  a 


FIG.  72. — The  lymphatic  vessels.  The  thoracic  duct  occupies  the  middle  of  the 
figure.  It  lies  upon  the  spinal  column,  at  the  sides  of  which  are  seen  portions  of  the 
ribs  (i).  a,  the  receptacle  of  the  chyle  ;  I,  the  trunk  of  the  thoracic  duct,  opening  at 
c  into  the  junction  of  the  left  jugular  (f}  and  subclavian  (g)  veins  as  they  unite  into 
the  left  innominate  vein,  which  has  been  cut  across  to  show  the  thoracic  duct  running 
behind  it;  d,  lymphatic  glands  placed  in  the  lumbar  regions;  A,  the  superior  vena 
cava  formed  by  the  junction  of  the  right  and  left  innominate  veins. 

temporary  abiding  place.     Leading  from  these  lymph  spaces 
are  delicate,  thm-walled  tubes,  which  join  together  to  form 


LACTEALS.  11 

larger  trunks.  In  the  course  of  these  trunks  are  situated  knots 
or  beads,  called  lymph  glands,  which  are  filled  with  cells  re- 
sembling somewhat  the  white  blood  corpuscles. 
These  glands  are  apparently  for  the  purpose  of 
supplying  white  corpuscles,  and  also  of  filter- 
ing the  lymph  and  destroying,  if  possible,  any 
foreign  materials,  such  as  bacteria,  which 
may  have  been  absorbed  from  the  tissues. 
The  lymph  trunks  join  together  to  form  still 
larger  trunks  which  finally  empty  as  single 
trunks,  one  upon  each  side  of  the  neck,  into 
the  subclavian  veins.  The  walls  of  the  lym- 
phatic tubes  are  exceedingly  thin  and  the 
tubes  themselves  can  only  be  readily  found 
when  they  are  distended  with  colored  liquid. 
They  are  richly  supplied  with  valves  which 
allow  the  contents  to  flow  only  from  the  tissues 
toward  the  heart. 

Since   the   lymphatic  vessels   take   up    or 
absorb  the  excess  of  liquid  drained  from  the      FIG.  73.— Valves 

of  lymphatics.  (Sap- 

blood   and   also    the    effete    matters    of  the    pey.) 
various  organs,  they  are  frequently  called  the  absorbents. 

Lacteals,  about  which  we  have  already  learned,  are  the 
lymphatics  of  the  small  intestine  (p.  125),  but  they  are 
larger  than  the  lymphatics  of  the  rest  of  the  system  since  the 
absorption  into  and  circulation  through  them  is  much  greater. 
The  great  lymphatic  trunk  which  receives  the  lymph  from 
the  lower  limbs  and  the  food  materials  absorbed  from  the  in- 
testinal tract  is  called  the  thoracic  duct  and  enters  the  left 
subclavian  vein. 

Histology  of  Lymph. — Pure  lymph  is  a  colorless,  watery- 
looking  liquid  ;  examined  with  a  microscope  it  is  seen  to  con- 


1 62  THE  HUM4N  BODY. 

tain  numerous  pale  corpuscles  exactly  like  the  white  blood 
corpuscles.  These  are  derived  in  large  part  from  the  blood, 
but  also  from  the  glands  through  which  the  lymph  comes. 

Chemistry  of  Lymph. — Lymph  is  not  quite  so  heavy  as 
blood,  though  heavier  than  water.  It  may  be  described  as 
blood  minus  its  red  corpuscles  and  considerably  diluted,  but  of 
course' in  various  parts  of  the  body  it  contains  minute  quanti- 
ties of  substances  derived  from  neighboring  tissues. 

Summary. — The  lymph  is  a  liquid  in  which  the  tissues  of 
the  body  live ;  it  is  derived  from  the  blood,  and  affords  the 
immediate  nourishment  of  the  great  majority  of  the  living 
cells  of  the  body ;  the  excess  of  it  is  finally  returned  to  the 
blood,  which  thus  indirectly  nourishes  the  cells  by  keeping 
up  the  stock  of  lymph.  The  lymph  itself  moves  slowly,  but 
is  constantly  renovated  by  the  blood.  The  blood  is  kept  in 
rapid  movement  by  the  heart,  and  besides  containing  a  store 
of  new  food  matters  for  the  lymph,  absorbs  from  it  the  gaseous 
waste  products  of  the  various  cells. 


CHAPTER  XIV. 
THE  ANATOMY  OF  THE  CIRCULATORY  ORGANS. 

The  Organs  of  Circulation  are  the  heart  and  the  blood 
vessels.  There  are  two  distinct  systems  of  blood  vessels  in 
the  body,  both  connected  with  the  heart ;  one  system  carries 
blood  to,  through,  and  from  the  lungs,  and  is  known  as  the 
pulmonary  ;  the  other  guides  its  flow  through  all  the  remain- 
ing organs,  and  is  known  as  the  systemic. 

General  Statement. — During  life  the  pumping  of  the  heart 
keeps  the  blood  flowing  rapidly  through  the  blood  vessels  ; 
these  paths  it  never  leaves  except  in  cases  of  disease  or  injury. 

The  blood  vessels  form  a  continuous  system  of  closed  tubes 
comparable  in  a  certain  way  to  the  water  mains  of  a  city ;  the 
heart  corresponds  to  the  reservoir,  the  great  artery  (aorta), 
with  its  branches,  to  the  main  aqueduct  and  branch  pipes. 
The  course  of  the  blood  differs,  however,  essentially  from 
that  of  the  water  supplied  to  a  city,  since  the  blood  is  carried 
back  to  the  heart.  There  is  at  any  instant  only  a  small 
amount  in  the  heart,  but  this  is  steadily  replaced  by  an  inflow 
as  fast  as  it  is  forced  out. 

General  Functions  of  the  Parts  of  the  Circulatory  Sys- 
tem.— The  blood  system  is  closed  *  except  at  two  points,  one 

*  In  the  spleen  only  is  there  a  break  in  the  continuity  of  the  blood 
vessels.  The  blood  escapes  from  the  open  ends  of  the  blood  vessels, 
flows  through  a  meshwork  of  tissue  cells,  and  re-enters  the  blood  vessels 
at  the  end  of  a  minute  distance. 

163 


164 


THE  HUMAN  BODY. 


on  each  side  of  the  neck,  where  lymph  vessels  pour  the  excess 
of  lymph  back  into  the  veins.  Valves  at  these  two  points  let 
lymph  flow  into  the  blood  vessels,  but  will  not  allow  blood 
to  flow  out.  Accordingly  everything  which  leaves  the  blood 
must  do  so  by  oozing  through  the  walls  of  the  blood  vessels, 
and  everything  which  enters  it  must  do  the  same,  ex- 
cept matters  conveyed  in  by  the  lymph  at  the  points 
above  mentioned.  This  interchange  through  the  walls 
of  the  vessels  takes  place  only  in  the  capillaries.  The 
capillaries,  though  far  the  smallest  tubes  in  the  vascular 
system,  are  the  really  important  parts.  The  heart,  arter- 
ies, and  veins  are  merely  arrangements  for 
keeping  the  blood  flowing  through  the 
capillaries.  It  is  while  flowing  through 
these  and  soaking  through  their  walls 
that  the  blood  does  its  physiological  work. 
Diagram  of  the  Circulatory  Organs.— 
The  general  relationship  of  the  heart  and 
blood  vessels  may  be  gathered  from  the 
accompanying  diagram  (Fig.  74).  The 
heart  is  essentially  a  bag  with  muscular 
walls,  internally  divided  into  four  cham- 
bers (d,  g,  e,f).  The  upper  two  (</and 
e)  receive  blood  from  vessels  opening  into 
them  known  as  veins.  Thence  the  blood 
passes  on  to  the  remaining  chambers  (^ 
which  have  very  muscular  walls,  and,  by  forcibly  con- 
tracting, drive  the  blood  out  into  communicating  vessels  (i 
and  b)  known  as  arteries.  The  big  arteries  divide  into 
smaller,  these  into  still  smaller  (Plate  IV),  until  the  branches 
become  too  small  to  be  traced  by  the  unaided  eye.  The 
smallest  branches  are  the  capillaries,  through  which  the  blood 


FIG.  74.—  The   heart 


blood  vessels  diagram- 
matically  represented. 


THE  POSITION  OP  THE  HEART.  165 

flows  into  the  veins,  which  in  turn  convey  it  back  to  the  heart. 
At  certain  points  in  the  course  of  the  veins  valves  are  placed, 
to  prevent  a  back  flow.  This  alternating  reception  of  blood  at 
one  end  of  the  heart  and  its  ejection  from  the  other  occurs  in 
men  about  seventy  times  a  minute  during  health. 

The  Position  of  the  Heart. — The  heart  (h,  Fig.  4)  lies 
in  the  chest,  immediately  above  the  diaphragm  and  opposite 
the  lower  two  thirds  of  the  breast  bone.  It  is  conical  in  form 
and  lies  with  its  base  or  broader  end  turned  upward  and  pro- 
jecting a  little  to  the  right  of  the  sternum.  Its  narrow  end  or 
apex  may  be  felt  beating  between  the  cartilages  of  the  fifth  and 
sixth  ribs  to  the  left  of  the  sternum.  The  position  of  the 
heart  in  the  body  is,  therefore,  oblique.  It  does  not,  how- 
ever, lie  on  the  left  side,  as  is  so  commonly  believed,  but  very 
nearly  in  the  middle  line,  with  the  upper  part  inclined  to  the 
right,  and  the  lower  (which  may  be  more  easily  felt  beating — 
hence  the  common  belief  )  to  the  left. 

The  Pericardium. — The  heart  is  surrounded  by  a  loose 
conical  bag  (pericardium)  composed  of  connective  tissue  and 
attached  by  its  broad  lower  part  to  the  upper  surface  of  the 
diaphragm.  The  pericardium  is  lined  by  a  smooth  serous 
membrane  like  that  lining  the  abdominal  cavity,  which  is  con- 
tinued over  the  heart  itself  and  adheres  closely  to  it.  In  the 
space  between  the  pericardium  and  the  heart  is  a  small  quan- 
tity of  liquid  which  moistens  the  contiguous  surfaces,  and 
thereby  diminishes  the  friction  which  would  otherwise  occur 
during  the  movements  of  the  heart. 

NOTE. — Sometimes,  especially  in  rheumatic  fever,  the  peri- 
cardium becomes  inflamed  (pericarditis).  In  the  earlier  stages 
of  this  inflammation  the  rubbing  surfaces  on  the  outside 
of  the  heart  and  the  inside  of  the  pericardium  become  rough- 
ened, and  their  friction  produces  a  sound  which  can  be  heard. 


1 66  THE  HUMAN  BODY. 

In  later  stages  great  quantities  of  liquid  may  accumulate 
in  the  pericardium  and  seriously  impede  the  heart's  beat. 

The  Cavities  of  the  Heart. — On  opening  the  heart  (Fig. 
74,  p.  164)  it  is  found  to  be  divided  into  completely  separate 
right  and  left  halves  by  a  longitudinal  partition  (septum)  which 
runs  from  about  the  middle  of  the  base  to  a  point  a  little  to 
the  right  of  the  apex.  Each  of  the  chambers  on  the  sides  of 
the  septum  is  divided  transversely  into  a  thinner  basal  portion 
into  which  veins  open  (auricle)  and  a  thicker  apical  portion 
from  which  arteries  arise  (ventricle) .  The  heart  cavity  thus 
consists  of  a  right  auricle  and  ventricle  and  a  left  auricle 
and  ventricle,  each  auricle  communicating  with  the  ventricle 
on  its  own  side  by  an  auricula-ventricular  orifice.  There  is 
no  direct  communication  through  the  septum  between  the 
opposite  sides  of  the  heart.  To  get  from  one  side  to  the  other 
the  blood  must  leave  the  heart  and  pass  through  a  set  of 
capillaries,  as  may  readily  be  seen  by  tracing  the  course  of  the 
vessels  in  Fig.  74. 

The  Vessels  Connected  with  the  Different  Chambers 
of  the  Heart. — One  big  artery,  called  the  aorta,  springs  from 
the  left  ventricle.  It  runs  down  to  the  pelvis,  giving  off 
many  branches  on  its  way,  and  then  divides  into  two  arteries, 
one  going  to  each  side,  which  by  their  branches  supply 
pelvis  and  legs. 

Its  big  branches  divide  into  smaller  and  these  into  still 
smaller  and  spread  through  the  whole  body,  to  muscles, 
bones,  skin,  brain,  stomach,  intestines,  liver,  kidneys,  etc., 
until  they  finally  end  in  the  systemic  capillaries.  The  sys- 
temic veins  collect  the  blood  from  the  capillaries  of  the  differ- 
ent organs,  and  unite  to  form  the  upper  and  lower  hollow  veins 
(the  superior  and  inferior  vena  cava).  These  carry  the  blood 
to  the  right  auricle ;  thence  it  enters  the  right  ventricle  from 


SUMMARY. 


167 


which  arises  one  vessel,  the  pulmonary  artery.  The  pulmonary 
artery  divides  into  two  branches,  one  for  each  lung ;  each 
branch  splits  up  into  minute 
arteries  in  its  own  lung, 
which  end  in  the  pulmonary 
capillaries.  From  the  pul- 
monary capillaries  the 
blood  of  each  lung  is  col- 
lected into  two  pulmonary 
veins,  which  open  into  the 
left  auricle. 

Summary. — One  artery, 
the  aorta,  arises  from  the 
left  ventricle.  The  blood 
carried  out  by  the  aorta 
passes  through  the  capilla- 
ries in  the  tissues,  returns 
by  the  upper  and  lower 
venae  cavae  to  the  right 

auricle,  goes     tO     the   right      FlG.  7S._FRONT  V.EW  o7T7E   HEART  AND 
,    .    i  j         ,1  GREAT  VESSELS. 

ventricle,       and      thence     ~, 

I  he   pulmonary   artery   has   been  cut   short 
through       the        pulmonary    dose.to  its  ori«in-    .'rri«ht  ventricle;  2,   left 


artery  to  the  lungs. 


ventricle  ;    3,   root  of  the  pulmonary  artery  ;  4, 
rpi         4',  arch  of  the  aorta;  4".  the  descending  thoracic 
^    aorta;  5,  part  of  the  right  auricle;  6,  part  of  the 
.       left  auricle  ;  7,  7',  innominate  veins  joining  to 
blood,    Carried    by  the   pill-    form  the  vena  daVa  superior  ;  »,  inferior  vena 

cava  ;  9,    one   of  the   large   hepatic  veins  ;  X» 

monary     artery      from      the    placed  in  the  right  auriculo-ventncular  groove, 

points  to  the  right  or  posterior  coronary  artery; 

right  Ventricle  Of  the  heart,     X,  X,  placed  in   the  anterior  interventricular 

groove,  indicate  the  left  or  anterior  coronary 

passes  through   the   capil-  arterv- 

laries  of  the  lungs,  returns  to  the  left  auricle  by  the  pul- 
monary veins,  enters  the  left  ventricle,  and  begins  its  flow 
again  through  the  aorta. 

How  the  Heart  is  Nourished. — The  heart  is  a  hard  working 
organ,  and  needs  an  abundant  supply  of  nourishment ;  accord- 


1 68 


THE  HUMAN  BODY. 


ingly    its    walls  are  permeated  by  a  very  close  network  of 
capillary  blood  vessels.      The  blood  enters  (Fig.  76)  through 


Sd 


Mpl 


Mpm 


FIG.  76.— The  left  ventricle  and  the  commencement  of  the  aorta  laid  open.  Mpm, 
Mpl,  the  papillary  muscles.  From  their  upper  ends  are  seen  the  chordae  tendinese 
proceeding  to  the  edges  of  the  flaps  of  the  mitral  valve.  The  opening  into  the 
auricle  lies  between  these  flaps.  At  the  beginning  of  the  aorta  are  seen  its  three 
pouch-like  semilunar  valves. 

the  right  and  left  coronary  arteries  (the  first  two  branches  of 
the  aorta)  and  leaves  by  the  coronary  veins,  which  carry  it 
to  the  right  auricle. 


AURICULO-VENTRICULAR   VALVES.  169 

The  Auriculo- Ventricular  Valves. — Between  each  auricle 
of  the  heart  and  the  ventricle  of  the  same  side  are  found 
valves  which  allow  blood  to  pass  from  the  auricle  to  the  ven- 
tricle, but  prevent  any  return.  These  valves  are  known  as 
the  tricuspid  and  mitral  valves.  The  mitral  valve  (Fig.  76) 
consists  of  two  flaps  fixed  by  their  bases  to  the  margins  of 
the  opening  between  the  left  auricle  and  the  left  ventricle. 
Their  unattached  edges  hang  down  into  the  ventricle  when 
it  is  being  filled  and  have  fixed  to  them  a  number  of  stout 
connective-tissue  cords,  the  chorda  tendinece.  These  in  turn 
are  attached  to  muscular  elevations,  the  papillary  muscles 
{Mpm  and  Mpl)  on  the  interior  of  the  ventricle.  The  cords 
are  long  enough  to  let  the  valve  flaps  rise  into  a  transverse 
position  and  thus  to  close  the  opening*  between  auricle  and 
ventricle.  The  tricuspid  valve  is  like  the  mitral,  but  with 
three  flaps  instead  of  two. 

Semilunar  Valves. — These  are  six  in  number,  three  at  the 
mouth  of  the  aorta  (Fig.  76),  and  three  at  the  mouth  of  the 
pulmonary  artery.  Each  is  a  strong  crescentic  pouch  fast- 
ened by  its  longer  edge,  with  its  free  edge  turned  away  from 
the  heart.  When  the  valves  are  closed,  their  free  edges  meet 
across  the  vessel  and  prevent  blood  from  flowing  back  into 
the  ventricle. 

The  Course  of  the  Main  Arteries  of  the  Body  (Fig.  77). 
— The  aorta  after  leaving  the  left  ventricle  makes  an  arch 
(#A)  with  its  convexity  towards  the  head.  From  the  begin- 
ning of  this  arch  arise  the  coronary  arteries,  which  carry 
blood  into  the  walls  of  the  heart.  From  the  convexity  of 
the  arch  spring  three  large  arterial  trunks,  the  innominate,  the 
left  common  carotid  (cr),  and  the  left  subclavian  (sji").  The 

*  This  opening  lies  behind  the  opened  aorta  (Sp]  and  cannot  be  seen 
in  the  figure. 


1 70  THE  HUMAN  BODY. 

innommaie  artery  soon  divides  into  the  right  subclavian  (sd) 
and  the  right  common  carotid  (a/).  Each  common  carotid 
runs  up  the  neck  on  its  own  side  and  divides  into  branches 
for  the  neck,  face,  scalp  and  brain.  Each  subclavian  gives 
off  a  branch,  the  vertebral  artery,  which  passes  to  the  b^ain 
through  the  transverse  processes  of  the  cervical  vertebrae 
(Figs.  13  and  14,  p.  25).  The  main  branch  of  the  sub- 
clavian continues  across  the  arm  pit  as  the  axillary  artery 
(A^)  and  then  runs  toward  the  elbow  as  the  brachial  artery 
(B).  Just  above  the  elbow  it  divides  into  the  radial  and 
ulnar  arteries  (R,  u),  which  supply  the  fore-arm  and  end  in 
small  branches  for  the  hand. 

Beyond  its  arch  the  aorta  runs  close  to  the  spinal  column 
as  the  thoracic  aorta  (A/),  which  gives  off  branches  to  the 
walls  and  some  of  the  organs  of  the  chest.  The  vessel  then 
passes  through  the  diaphragm,  and  continues  as  the  abdomi- 
nal aorta  (&ab]  to  the  lower  part  of  the  abdomen.  The  main 
branches  of  the  abdominal  aorta  are:  (i)  the  cceliac  axis, 
which  divides  into  branches  for  the  stomach,  liver,  and 
spleen ;  (2)  the  upper  and  lower  mesenteric  arteries,  which 
supply  the  intestines  with  blood ;  (3)  the  renal^arteries  (K), 
which  supply  the  kidneys. 

The  two  trunks  into  which  the  posterior  end  of  the  ab- 
dominal aorta  divides  (Ai)  are  the  common  iliac  arteries. 
Each  gives  off  branches  in  the  pelvis,  and  then  continues 
along  the  thigh  as  the  femoral  artery  (C) ;  this  runs  to  the 
knee  joint,  behind  which  it  is  called  the  popliteal  artery  (Po). 
The  popliteal  artery  divides  into  the  peroneal  (Pe)  and  tibial 
(Ta,  Tp~)  arteries,  which  supply  the  lower  leg  and  the  foot. 

The  Properties  of  the  Arteries. — Two  fundamental  facts 
must  be  borne  in  mind  in  connection  with  the  arteries : 
first,  that  they  are  highly  elastic  and  extensible,  much  like  a 


14- 


PLATE   IV.— THE  CHIEF  ARTERIES  AND  VEINS  OF  THE  BODY. 


EXPLANATION  OF  PLATE  IV 
THE  CIRCULATORY  ORGANS. 

The  arteries  (except  the  pulmonary)  and  the  left  side  of  the  heart 
are  colored  red;  the  veins  (except  the  pulmonary)  and  the  right  half  of 
the  heart  blue.  On  the  limbs  of  the  left  side  the  arteries  are  omitted  and 
only  the  superficial  veins  are  shown. 

1.  Aorta,  near  its  origin  from  the  left  ventricle  of  the  heart. 

2.  Lower  end  of  aorta. 

3.  Iliac  artery. 

4.  Femoral  artery. 

5.  Popliteal  artery  ;  the   continuation  of  the   femoral  which   passes  behind    the 

knee  joint. 

6.  7.  The  main  trunks  (anterior  and  posterior  tibial  arteries  into  which  the  pop- 

liteal divides). 

8.  Subclavian  artery. 

9.  Brachial  artery. 

10.  Radial  artery. 

11.  Ulnar  artery. 

12.  Common  carotid  artery. 

13.  Facial  artery. 

14.  Temporal  artery. 

15.  Right  side  of  heart,  with  superior  vena  cava  joining  it   above,  and    inferior 

vena  cava  (16)  passing  up  to  it  from  below. 

17.  Innominate  vein,  formed  by  the  union  of  subclavian  and  jugular  veins.     The 

right  and  left  innominate  veins  unite  to  form  the  superior  cava. 

18.  Left  internal  jugular  vein. 
IQ.  Axillary  vein. 

20.  Basilic  vein. 

21.  Cephalic  vein. 

22.  Median  vein. 

23.  Radial  vein. 

24.  Ulnar  vein. 

25.  Median  vein. 

26.  Iliac  vein. 

27.  Femoral  vein. 

28.  Long  saphenous  vein. 

29.  The  kidney  ;  attached  to  it  are  seen  the  renal  artery  and  vein. 

30.  Branches  of  the  pulmonary  arteries  and  veins  in  the  iuag. 


THE  MAIN  ARTERIES   OF  THE  BODY. 


171 


FIG.  77. — The  main  arteries  of  the  body.  Crd  and  Crs,  right  and  left  coronary  ar- 
teries of  the  heart,  cut  short  near  their  origin;  A  a  and  aA,  aortic  arch;  At,  thoracic 
aorta;  Aa&,  abdominal  aorta;  K,  renal  artery;  Sd,  right,  and  Ssf,  left  subclavian; 
Cd,  right,  and  Cs,  left  carotid;  Ax,  axillary  artery;  B,  brachial  artery;  £/,  ulnar 
artery;  R,  radial  artery;  At,  common  iliac  artery;  /,  external  iliac  artery;  C,  femoral 
artery;  Po,  popliteal  artery;  Tat  anterior,  and  TJ>,  posterior  tibial  artery;  /V,  peroneal 
artery. 


172 


THE  HUMAN  BODY. 


piece  of  rubber  tubing  of  the  same  size;  second,  that  they 
have  rings  of  muscular  tissue  in  their  walls.  When  these 
contract,  the  bore  of  the  artery,  and  consequently  the  amount 
of  blood  which  flows  through  it,  is  diminished.  When  they 
relax,  the  bore  of  the  artery  is  increased,  and  more  blood 
passes  along  it  to  the  capillaries. 

The  Capillaries. — The  smallest  arteries   (arterioles*}  pass 


FIG.  78. 


FIG. 


FIG.  78. — Diagrammatic  representation  of  a  capillary  seen  from  above  and  in  sec- 
tion, a,  the  wall  of  the  capillary  with.  &,  the  nuclei;  <r,  nuclei  belonging  to  the 
connective  tissue  in  which  the  capillary  is  supposed  to  be  lying;  d,  the  canal  of  the 
capillary. 

FIG.  79. — Transverse  section  through  a  small  artery  and  vein.  A,  artery;  V,  vein; 
e.  epithelial  lining;  m,  middle  muscular  and  elastic  coat,  thick  in  the  artery,  much 
thinner  in  the  vein;  a,  outer  coat  of  areolar  tissue  (magnified  350  diameters). 


into  the  capillaries,  which  have  very  thin  walls,  and  form  a 
close,  network  in  all  parts  of  the  body.     Tfre  average  diara- 


THE  VEINS.  173 

eter  of  a  capillary  vessel  is  so  small  that  only  one  or  two 
blood  corpuscles  can  pass  through  it  abreast,  and  in  many 
parts  the  capillaries  lie  so  close  together  that  a  pin's  point 
cannot  be  inserted  between  two  of  them,  as,  for  example,  in 
the  deep  layers  of  the  skin,  which  cannot  be  pricked  without 
drawing  blood.  Their  immense  number,  however,  much 
more  than  compensates  for  their  size.  It  is  while  flowing  in 
these  delicate  tubes  that  the  blood  does  its  nutritive  work, 
for  here  only  can  the  liquid  containing  nourishment  exude 
from  the  blood  through  the  thin  walls  to  bathe  the  various 
tissues.  Imagine  a  crumpled  mass  of  the  finest  lace,  with  all 
its  threads  consisting  of  hollow  tubes,  and  diminished  twenty 
times  in  size,  and  you  will  have  some  idea  of  the  size  and 
richness  of  distribution  of  the  capillaries. 

The  walls  of  the  capillaries  are  formed  of  a  single  layer  of 
flat  cells  and  are  really  a  continuation  of  the  lining  membrane 
of  the  arteries,  veins,'  and  heart,  which  thus  becomes  con- 
tinuous ^throughout  the  circulatory  system  with  the  exception 
of  the  spleen. 

The  Veins. — The  smallest  veins  arise  from  the  capillary 
network  and  unite  to  form  larger  and  larger  trunks.  One  of 
these  usually  runs  along  with  the  main  artery  of  the  part,  but 
there  are  ordinarily  several  other  large  veins  just  beneath  the 
skin.  This  is  especially  the  case  in  the  limbs,  the  main  veins 
of  which  are  superficial,  and  can  in  many  persons  be  seen  as 
faint  blue  lines.  The  walls  of  the  veins  are  similar  in 
structure  to  those  of  the  arteries,  except  that  they  are 
thinner. 

Why  the  Large  Arteries  usually  lie  deep. — The  heart 
pumps  the  blood  with  great  force  into  the  arteries,  and  when 
an  artery  is  cut  very  rapid  and  dangerous  bleeding  occurs  ; 
the  veins,  if  cut,  do  not  bleed  nearly  so  violently  as  an  artery 


THE  HUMAN  BODY. 


of  the  same  size.      Hence  it  is  less  dangerous  to  have  a  large 
vein  than  a  large  artery  close  under  the  skin. 

The  Valves  of  the  Veins. — Except  the  pulmonary  artery 
and  the  aorta,  which  have  the  semilunar  valves  at  their  origin, 


FIG.  80. — A  small  portion  of  the  capillary  network  as  seen  in  the  frog's  web  when 
magnified  about  25  diameters.  «,  a  small  artery  feeding  the  capillaries ;  z/,  &,  small 
veins  carrying  blood  back  from  the  latter. 

arteries  have  no  valves.  Most  veins,  on  the  contrary,  con- 
tain many  valves  formed  by  pouches  of  their  lining,  which 
resemble  in  form  the  semilunar  valves  of  the  aorta  and  the 
pulmonary  artery.  These  valves  permit  blood  to  flow  only 


THE  VALVES  OF  THE  VEINS.  1 75 

towards  the  heart,   for  a  current    in   that   direction   (upper 
diagram,  Fig.  82)  presses  the  valve  close  against  the  side  of 


FIG.  Si. — Circulation  in  frog's  foot  (under  microscope).  A,  walls  of  capillaries; 
£,  tissue  of  web  lying  between  the  capillaries;  C,  cells  of  epidermis  covering  web 
(these  are  only  shown  in  the  right-hand  and  lower  part  of  the  field;  in  the  other  parts 
of  the  field  the  focus  of  the  microscope  lies  below  the  epidermis);  D,  nucle;'  of  these 
epidermic  cells;  £,  pigment  cells  contracted,  not  partially  expanded;  F,  red  blood 
corpuscle  (oval  in  the  frog)  passing  along  capillary — nucleus  not  visible  ;  G,  another 
corpuscle  squeezing  its  way  through  a  capillary,  the  canal  of  which  is  smaller  than 
its  own  transverse  diameter;  //,  another  bending  as  it  slides  round  a  corner;  Ky 
corpuscle  in  capillary  seen  through  the  epidermis  ;  /,  white  blood  corpuscle. 


i?6  THE  HUM4N  BODY. 

the  vessel,  and  meets  with  no  obstruction  from  it.     Should 
any  back  flow  be  attempted,  however,  the  current  closes  up 
*  the  valve    and  bars    its    own   passage 

C          ^-^-^  H   (lower  figure).     These  valves  are  most 

numerous  in  superficial  veins  and  those 
of  muscular   parts.      They  are   found 
especially     where     two     veins     join. 
FIG.  82.— Diagram  to  iiius-  Usually  the    vein    is   a   little    dilated 

trate  the  mode  of  action  of  the 

valves  of  the  veins,  c,  the  capii- OppOSite  a  valve,  and  hence  in  parts 

lary;  H,  the  heart   end   of  the     rr 

vessel<  where  the  valves  are  numerous  has  a 

knotted  look.  On  tying  a  cord  tightly  round  the  forearm, 
so  as  to  stop  the  flow  in  its  subcutaneous  veins  and  cause  their 
dilatation,  the  points  at  which  valves  are  placed  can  be  recog- 
nized by  their  swollen  appearance. 

The  Course  of  the  Blood. — From  what  has  been  said  it  is 
clear  that  the  movement  of  the  blood  is  a  circulation.  Start- 
ing from  any  one  chamber  of  the  heart  it  will  in  time  return 
to  it ;  but  to  do  this  it  must  pass  through  at  least  two  sets  of 
capillaries,  one  of  which  is  connected  with  the  aorta,  and  the 
other  with  the  pulmonary  artery.  In  this  circuit  the  blood 
returns  to  the  heart  twice ;  leaving  the  left  side  it  returns  to 
the  right,  and  leaving  the  right  it  returns  to  the  left  There 
is  no  road  for  it  from  one  side  of  the  heart  to  the  other  except 
through  a  capillary  network.  Moreover,  it  always  leaves 
from  a  ventricle  through  an  artery,  and  returns  to  an  auricle 
through  a  vein. 

There  is  then  really  only  one  circulation  ;  but  it  is  not 
uncommon  to  speak  of  the  flow  from  the  left  side  of  the  heart 
to  the  right  through  most  of  the  body  as  the  systemic  or 
greater  circulation,  and  of  the  flow  from  the  right  to  the  left 
through  the  mngs  as  the  pulmonary  or  lesser  circulation.  But 
since,  after  completing  either  of  these,  the  blood  is  not  again 


THE  PORTAL   CIRCULATION. 


177 


at  the  point  from  which  it  started,  but  is  separated  from  it  by 
the  septum  of  the  heart,  neither  is  a  "circulation"  in  the 
proper  sense  of  the  word,  for  a  circulation  implies  that  any 
object  is  at  the  end  of  its  course  where  it  was  at  the  beginning. 


FIG.  83 — The  portal  vein  and  its  branches.  /,  liver,  under  surface;  gb,  gall  blad- 
der; st,  stomach;  sp,  spleen;/,  pancreas;  du,  duodenum;  ac,  ascending  colon;  cd, 
descending  colon;  a,  £,  c,  d,  e,  the  portal  vein  and  its  branches.  Portions  of  the  duo- 
denum and  colon  have  been  removed. 

The  Portal  Circulation. — That  portion  of  the  blood  which 
goes  through  the  stomach  and  intestines  has  to  pass  through 
three  sets  of  capillaries  before  it  can  return  there.  It  leaves 
the  left  ventricle  of  the  heart  through  the- aorta,  traverses  the 
capillaries  of  the  stomach  and  intestines,  is  carried  by  the 
portal  vein  into  the  liver,  and  here  passes  through  the  capil- 
laries of  the  portal  vein,  which  in  the  liver  branches  like  an 
artery.  From  these  it  is  collected  by  the  hepatic  veins  and 


THE  HUMAN  BODY. 


poured  into  the  inferior  vena  cava,  which  carries  it  to  the 
right  auricle,  so  that  it  has  still  to  pass  through  the  pulmona-  y 
capillaries  to  get  back  to  the  left  side  of  the  heart.  The 
portal  vein  is  the  only  one  in  the  human  body  which  thus 
like  an  artery  feeds  a  capillary  network.  The  flow  from  the 
stomach  and  intestines  through  the  liver  to  the  inferior  vena 
cava  is  often  spoken  of  as  the  portal  circulation. 

Diagram  of  the  Circulation.  —  Since  the  two  halves  of  the 
heart,  although  placed  in  proximity  in  the  body,  are  com- 
pletely separated  from  one  another 
by  an  impervious  partition,  we  may 
conveniently  represent  the  course  of 
the  blood  as  in  the  accompanying 
diagram  (Fig.  84),  in  which  the 
right  and  left  halves  of  the  heart  are 
represented  at  different  points  in  the 
vascular  system.  Such  a  diagram 
makes  it  clear  that  the  heart  is  really 
two  pumps  working  side  by  side, 
each  engaged  in  forcing  blood  to 
the  other.  Starting  from  the  left 
auricle  (/#)  we  trace  the  flow 
through  the  left  ventricle,  along 
the  branches  of  the  aorta  into  the 

systemic  capillaries  (w°'  Ihence 

itepreente   by    through  the  systemic  veins  (vc~)  into 

the  right  and  left  halves  of  the 

heart,   which   are   separated   in      the    right    auricle     \rO)t     thence    intO 

the  diagram,     ra  and  rv,  right 

auricle  and  ventricle;  la  and  Iv,      the  right  ventricle   (rv),   through  the 

left  auricle   and   ventricle  ;  ao, 

aorta  ;  sc,  systemic  capillaries  :      rjulmOliarV    artery    (  P&)     tO    the 

vc,  venae  cavse;  pa,  pulmonary 


capillaries  (/O  along  the  pulmonary 
veins  (pv)  to  the  left  auricle,  into  the  left  ventricle  (&),  and 
again  into  the  aorta. 


ARTERIAL  AMD   VENOUS  BLOOD.  i?9 

Arterial  and  Venous  Blood. — The  blood  when  flowing  in 
the  pulmonary  capillaries  gives  up  carbon  dioxide  to  the  air, 
and  receives  oxygen  from  it.  Since  its  coloring  matter 
(haemoglobin)  forms  a  scarlet  compound  with  oxygen  (oxy- 
hcemoglobin} ,  the  blood  which  flows  to  the  left  auricle  through 
the  pulmonary  veins  is  bright  red.  This  color  it  maintains 
until  it  reaches  the  systemic  capillaries,  when  it  loses  oxygen 
and  becomes  dark  purple  because  of  the  excess  of  the  darker 
colored  haemoglobin.  In  the  lungs  the  haemoglobin  becomes 
again  oxidized.  The  bright  red  blood,  rich  in  oxygen  and 
poor  in  carbon  dioxide,  is  known  as  •'arterial  blood,"  and 
the  dark  red  as  "  venous  blood."  It  must  be  borne  in  mind 
that  the  terms  apply  to  the  character  of  the  blood,  and  that 
the  pulmonary  veins  contain  arterial  blood,  and  the  pulmonary 
arteries  contain  venous  blood.  The  change  from  arterial  to 
venous  takes  place  in  the  systemic  capillaries,  and  from 
venous  to  arterial  in  the  pulmonary  capillaries. 


CHAPTER  XV. 
THE  WORKING  OF  THE  HEART  AND  BLOOD  VESSELS. 

The  Beat  of  the  Heart  commences  as  a  contraction  of  the 
mouths  of  the  veins  which  open  into  the  auricles.  This  con- 
traction runs  over  the  auricles,  and  is  immediately  taken  up 
by  the  ventricles.  The  auricles  relax  the  moment  the  ven- 
tricles start  their  contraction.  Having  finished  their  contrac- 
tion, the  ventricles  begin  to  dilate,  and  then  for  some  time 
neither  they  nor  the  auricles  contract,  but  the  whole  heart  ex- 
pands. The  contraction  of  any  part  of  the  heart  is  known  as 
its  sys'to-le,  and  the  relaxation  as  its  di-asto-le.  Since  the 
two  sides  of  the  heart  work  synchronously,  the  auricles  to- 
gether and  the  ventricles  together,  we  may  describe  a  whole 
cardiac  period  or  ' '  heart  beat ' '  as  made  up  successively  of 
auricular  systole,  ventricular  systole,  and  pause.  In  the  pause 
the  heart  is  soft  and  flabby,  but  during  the  systole  it  becomes 
hard  and  so  diminished  in  size  that  the  ventricles  are  entirely 
emptied. 

The  Cardiac  Impulse. — The  human  heart  lies  with  its  apex 
touching  the  chest  wall  between  the  fifth  and  sixth  ribs  on 
the  left  side  of  the  breast-bone.  At  every  beat  a  sort  of  tap 
known  as  the  cardiac  impulse,  or  apex  beat,  may  be  felt  by 
placing  the  finger  at  that  point. 

1 80 


EVENTS  DURING  A  CARDIAC  PERIOD. 


181 


FIG.  85.  —  Transverse 
section  through  the  mid- 
dle of  the  ventricles  of  a 
dog's  heart  in  diastole 
and  in  systole. 


Events  occurring  within  the  Heart  during  a  Cardiac 
Period. — Let  us  commence  with  the  pause  at  the  end  of  the 
ventricular  systole.  At  this  instant  the 
semilunar  valves  in  the  orifices  of  the  aorta 
and  the  pulmonary  artery  are  closed  so 
that  no  blood  can  flow  back  from  these 
vessels.  The  whole  heart,  however,  is 
soft  and  distensible,  and  readily  yields  to 
blood  flowing  into  its  auricles  from  the 
pulmonary  veins  and  the  venae  cavae. 
This  blood  passes  on  through  the  open 
mitral  and  tricuspid  valves,  and  fills  up 
the  dilating  ventricles  as  well  as  the 
auricles.  As  the  ventricles  fill,  the  valve 
flaps  float  up  so  that  by  the  end  of  the 
pause  they  are  nearly  closed.  At  this  in- 
stant the  auricles  begin  to  contract  at  the  mouths  of  the  veins 
and  narrow  them  ;  the  relaxed  ventricles  oppose  little 
resistance,  and  hence  the  auricles  send  most  of  the  blood  into 
the  ventricles  and  but  little  back  into  the  veins.  When  the 
auricles  cease  their  contraction,  the  filled  ventricles  contract 
and  by  their  pressure  on  the  blood  within,  completely  close 
the  auriculo-ventricular  valves.  The  blood  in  each  ventricle 
is  now  imprisoned  between  the  auriculo-ventricular  valves 
behind  and  the  semilunar  valves  in  front.  The  former  cannot 
yield  on  account  of  the  chordae  tendineae  fixed  to  their  edges; 
the  semilunar  valves,  on  the  other  hand,  can  open  out- 
ward from  the  ventricle  and  let  the  blood  pass  on,  but 
they  are  kept  tightly  shut  by  the  pressure  of  the  blood  in 
the  aorta  and  pulmonary  artery.  The  contracting  ventricle 
tightens  its  grip  on  the  blood.  As  it  squeezes  harder  and 
harder,  its  pressure  on  the  blood  becomes  greater  than  the 


182 


THE  HUMAN  BODY. 


pressure  exerted  on  the  other  side  of  the  valves  by  the  blood 
in  the  aorta,  the  valves  are  forced  open,  and  the  blood  begins 
to  pass  out.  The  ventricle  continues  to  contract  until  it  has 


FIG.  86. — Diagram  to  illustrate  the  action  of  the  heart,  aur.,  auricle;  vent.,  ventri- 
cle; z/,  veins;  a,  aorta;  m,  mitral  valve;  j,  semilunar  valves  In  A,  auricle  contracting, 
ventricle  dilated,  mitral  valve  open,  semilunar  valves  closed.  In  B,  auricle  dilated, 
ventricle  contracting,  mitral  valve  closed,  semilunar  valves  open. 

completely  emptied  itself,  when  it  again  commences  to  relax. 
Blood  would  now  flow  back  into  it  from  the  arteries,  were  it 
not  that  this  back  current  instantly  catches  the  pockets  of  the 
semilunar  valves,  carries  them  back,  and  closes  the  valve  so 
as  to  form  an  impassable  barrier. 

Use  of  the  Papillary  Muscles. — In  order  that  the  contract- 
ing ventricles  may  not  force  blood  back  into  the  auricles,  it  is 
essential  that  the  flaps  of  the  mitral  and  tricuspid  valves  be 
held  together  across  the  openings  which  they  close,  and  not 
be  carried  back  into  the  auricles.  If  they  were  like  swinging 
doors  and  opened  both  ways  they  would  be  useless ;  they 
must  so  far  resemble  an  ordinary  door  as  only  to  open  in  one 
direction,  namely,  from  the  auricle  to  the  ventricle.  At  the 


SOUNDS  OF  THE  HEART.  183 

commencement  of  the  ventricular  systole  this  is  provided  for 
by  the  chordae  tendineae,  which  are  of  such  a  length  and  so 
arranged  as  to  keep  the  valve  flaps  shut  across  the  opening, 
and  to  maintain  their  edges  in  contact.  But,  as  the  contract- 
ing ventricles  shorten,  the  chordae  tendineae  would  be  slack- 
ened and  the  valve  flaps  pushed  up  into  the  auricle,  did  not 
the  little  papillary  muscles  prevent  this.  By  shortening  as 
the  ventricular  systole  proceeds,  they  keep  the  chordae  taut 
and  the  valves  closed. 

Sounds  of  the  Heart. — If  the  ear  is  placed  on  the  chest  of 
another  person  over  the  heart  region,  two  distinguishable 
sounds  will  be  heard  during  each  round  of  the  heart's  work. 
They  are  known  respectively  as  the  first  and  second  sounds  of 
the  heart.  The  first  is  of  lower  pitch,  lasts  longer  and  is  less 
sharp  than  the  second.  Vocally  their  character  may  be  toler- 
ably imitated  by  the  syllables  tub,  dup.  The  cause  of  the 
second  sound  is  the  closure  of  the  semilunar  valves.  The  first 
sound  takes  place  during  the  ventricular  systole,  and  is  prob- 
ably due  to  vibrations  of  the  tense  valve  flaps  and  the  ven- 
tricular wall.  In  many  forms  of  heart  disease  these  sounds 
are  modified  or  cloaked  by  additional  sounds  due  to  the 
roughened,  narrowed  or  dilated  cardiac  orifices,  or  to  the 
inefficiency  of  the  valves.  A  physician  often  gets  important 
information  as  to  the  nature  of  a  heart  disease  by  studying 
these  new  or  altered  sounds. 

Function  of  the  Auricles. — The  ventricles  have  to  do  the 
work  of  pumping  the  blood  through  the  blood  vessels.  Ac- 
cordingly their  walls  are  far  thicker  and  more  muscular  than 
those  of  the  auricles ;  the  left  ventricle,  which  has  to  force 
the  blood  over  most  of  the  body,  is  stouter  than  the  right, 
which  has  only  to  send  blood  around  the  comparatively  short 
pulmonary  circuit.  The  circulation  of  the  blood  is,  in  fact, 


1 84  THE  HUMAN  BODY. 

maintained  by  the  ventricles,  and  one  may  be  led  to  inquire 
what  is  the  use  of  the  auricles.  During  the  pause  of  the  heart 
the  blood  flows  on  through  the  auricles  into  the  ventricles, 
which  are  already  nearly  full  when  the  auricles  contract ;  this 
contraction  merely  completes  the  filling  of  the  ventricles. 
The  main  use  of  the  auricles  then  is  to  afford  a  reservoir  into 
which  the  veins  may  empty  while  the  comparatively  slow  ven- 
tricular contraction  is  taking  place. 

The  Work  Done  Daily  by  the  Heart.—'  <  The  <  work  done ' 
by  a  contracting  muscle  is  expressed  by  the  height  to  which  a 
weight  is  raised.  In  the  case  of  the  heart,  the  weight  raised 
is  the  amount  of  blood  contained  in  the  ventricles;  the  height 
to  which  that  weight  would  be  raised  is  the  height  of  intra- 
ventricular  blood-pressure  during  systole.  From  these  data  it 
is  easy  to  calculate  the  '  work '  done  at  each  systole,  and 
knowing  the  pulse-frequency,  the  average  per  hour  or  per  day 
is  also  known.  Admitting  for  the  left  ventricle  an  average 
discharge  of  120  grams,  and  a  systolic  pressure  of  2  meters, 
the  work  done  at  each  contraction  will  amount  to  150  gram- 
meters  ;  to  this  amount  we  may  add  50  grammeters  as  the 
work  done  by  the  right  ventricle  and  by  the  two  auricles, 
making  up  a  total  of  200  grammeters  or  \  kilogrammeter  as 
the  work  done  by  the  heart  at  each  beat.  With  a  pulse- 
frequency  of  72  per  minute  this  would  amount  to  864  kgm. 
per  hour,  or  more  than  20,000  kgm.  per  diem.  The  whole 
of  this  energy  is  expended  in  the  body,  partly  in  overcoming 
resistance  in  the  vascular  system,  and  partly  transformed  into 
and  discharged  as  heat ;  in  this  form  the  contractions  of  the 
heart  yield  about  -jfoth  of  the  total  daily  heat  production." — 
Waller. 

If  a  man  weighing  165  pounds  climbs  a  mountain  2500 
feet  high  the  muscles  of  his  legs  will  be  tired  at  the  end  of 


THE  NERYES  OF  THE  HEART.         185 

his  journey,  and  yet  in  lifting  his  body  that  height  they  have 
done  only  as  much  work  as  his  heart  does  every  day  without 
fatigue  in  pumping  his  blood. 

No  doubt  the  fact  that  more  than  half  of  every  round  of 
the  heart's  activity  is  taken  up  by  the  pause  during  which  its 
muscles  are  relaxed  and  its  cavities  filling  with  blood  has  a 
great  deal  to  do  with  the  patient  and  tireless  manner  in  which 
it  pumps  along,  minute  after  minute,  hour  after  hour,  and  day 
after  day,  from  birth  to  death. 

During  the  pause  between  contractions,  the  heart  muscle 
gets  its  rest ;  it  has  been  estimated  that  the  heart  muscle  does 
active  work  during  only  eight  hours  of  the  twenty-four  and 
rests  during  sixteen.  When  the  heart  beats  more  rapidly  the 
period  of  contraction  changes  but  little,  the  extra  beats  en- 
croaching upon  the  resting  time.  In  fever,  when  the  heart 
beat  is  much  more  rapid,  it  has  less  time  to  rest  and  is  liable 
to  become  exhausted  by  overwork  with  insufficient  recupera- 
tion. 

The  Nerves  of  the  Heart. — The  beat  of  the  heart  is  due 
to  the  contraction  of  the  muscle  fibres  making  up  its  wall. 
This  contraction  is  caused  by  nervous  impulses  received  from 
nerve  centres,  as  will  be  explained  later.  These  nerves  (in- 
trinsic heart  nerves)  are  in  close  connection  with  the  muscle 
fibres  and  tend  to  cause  them  to  contract  regularly  and  some- 
what rapidly.  Their  influence  is  modified  by  a  second  set  of 
nerves  (pneumogastric,  or 'vagus)  which  tend  to  make  the 
heart  beat  more  slowly,  that  is,  to  inhibit  the  action  of  the 
intrinsic  nerves.  A  third  set  (accelerator)  have  apparently 
the  power  of  quickening  the  heart's  action.  The  rate  and 
strength  of  the  beat  at  any  time  is  due  to  an  involuntary 
balancing  of  the  influences  of  the  first  two  sets  (and  possibly 
the  third)  to  meet  the  body's  needs.  The  need  of  oxygen 


1 86  THE  HUMAN  BODY. 

has  the  chief  influence  in  modifying  the  heart's  beat,  as  will 
be  seen  under  respiration. 

The  Pulse. — When  the  left  ventricle  of  the  heart  contracts 
it  forces  on  about  120  grams  of  blood  into  the  aorta,  which, 
with  its  branches,  is  already  full  of  blood.  The  elastic 
arteries  are  consequently  stretched  by  the  extra  blood.  This 
dilatation  of  an  artery  following  each  beat  of  the  heart  is 
called  the  pulse.  It  is  best  felt  on  arteries  which  lie  near  the 
surface  of  the  body,  as  the  radial  artery,  near  the  wrist,  and 
the  temporal  artery,  on  the  brow. 

Before  the  next  heart  beat  occurs,  the  arteries  by  their 
elasticity  have  forced  through  the  capillaries  as  much  blood 
as  the  aorta  received  during  the  preceding  ventricular  systole  ; 
consequently  they  shrink  again  during  the  pause,  just  as  a 
piece  of  rubber  tubing  with  a  small  hole  in  it,  when  overfilled 
with  water,  gradually  collapses  as  the  water  flows  out  of  it. 
The  next  beat  of  the  heart  again  overfills  and  expands  the 
arteries,  and  so  on.  Thus  at  each  heart  beat  there  is  a  dila- 
tation of  the  arteries  due  to  the  blood  sent  into  them  from 
the  ventricle,  and  between  each  beat  there  is  a  partial 
emptying  of  the  arteries,  due  to  their  forcing  some  of  their 
contents  into  the  capillaries. 

What  may  be  learnt  from  the  Pulse. — Since  the  pulse 
is  dependent  on  the  heart's  systole,  "  feeling  the  pulse"  gives 
a  convenient  means  of  counting  the  rate  of  the  heart  beat. 
To  the  skilled  touch,  however,  it  tells  much  more  ;  as,  for 
example,  a  readily  compressible  or  ' <  soft  pulse  ' '  shows  that 
the  heart  is  not  keeping  the  arteries  properly  filled  with  blood  ; 
a  tense  and  rigid  or  "  hard  pulse"  indicates  that  the  heart  is 
keeping  the  arteries  excessively  filled,  and  is  working  too  vio- 
lently. In  healthy  adults  the  pulse  rate  varies  from  sixty-five 
to  seventy-five  a  minute,  the  most  common  rate  being  seventy- 


CIRCULATION  OF  BLOOD  IN  FROG'S   WEB.         187 

two.  In  the  same  individual  it  is  faster  when  standing  than 
when  sitting,  and  when  sitting  than  when  lying  down.  Any 
exercise  or  excitement  increases  its  rate  temporarily.  A  sick 
person's  pulse  should  not  therefore  be  felt  when  he  is  nervous 
or  excited.  In  children  the  pulse  is  quicker  than  in  adults, 
and  in  old  age  slower  than  in  middle  life. 

The  Flow  of  the  Blood  in  the  Capillaries  and  Veins.— 
The  movement  of  the  blood  from  the  heart  is  intermittent, 
coinciding  with  each  systole  of  the  ventricles.  Before  it  reaches 
the  capillaries,  however,  this  rhythmic  movement  is  trans- 
formed into  a  steady  flow,  as  may  readily  be  seen  by  examin- 
ing with  a  microscope  thin  transparent  parts  of  various  animals, 
e.g.  the  web  of  a  frog's  foot,  a  bat's  wing,  or  the  tail  of  a 
small  fish.  In  consequence  of  the  steadiness  with  which  the 
capillaries  supply  the  veins  the  flow  in  them  is  also  unaffected 
by  the  beat  of  the  heart.  If  a  vein  is  cut  the  blood  wells  out 
uniformly,  whereas  a  cut  artery  spurts  out  in  powerful  jets 
which  correspond  with  the  contractions  of  the  ventricles. 

The  Circulation  of  the  Blood  as  Seen  in  the  Frog's 
Web. — There  is  no  more  fascinating  or  instructive  spectacle 
than  the  circulation  of  the  blood  in  the  thin  membrane 
between  the  toes  of  a  frog's  hind  limb  as  seen  with  the  micro- 
scope. Upon  focusing  beneath  the  outer  layer  of  the  skin,  a 
network  of  minute  arteries,  veins,  and  capillaries,  with  the 
blood  flowing  through  them,  comes  into  view  (Figs.  84  and 
86).  The  arteries  are  readily  recognized  by  the  fact  that  the 
flow  in  them  is  fastest  and  from  larger  to  smaller  branches. 
The  smallest  end  in  a  capillary  network,  the  channels  of  which 
are  all  nearly  equal  in  size.  In  the  veins  arising  from  the 
capillaries  the  flow  is  from  smaller  to  larger  trunks,  slower 
than  in  the  arteries,  but  faster  than  in  the  capillaries. 

The  Blood  flows  most  slowly  in  the  Capillaries  because 


1 88  THE  HUMAN  BODY. 

their  united  area  is  many  times  greater  than  tnat  of  the 
arteries  supplying  them,  so  that  the  same  quantity  of  blood 
flowing  through  them  in  a  given  time  has  a  wider  channel  to 
flow  in.  The  aggregate  area  of  the  veins  is  smaller  than  that 
of  the  capillaries,  but  greater  than  that  of  the  arteries  ;  there- 
fore the  rate  of  movement  in  them  is  intermediate. 

If  the  aggregate  areas  of  all  the  branches  of  the  circulatory 
system  were  taken,  beginning  at  the  origin  of  the  aorta,  we 
should  have  a  double  cone,  as  represented  in  Fig.  87.  Start- 
ing at  the  beginning  of  the  aorta  we  have  a  tube  one  inch  in 
diameter,  which  gradually  expands  because  of  the  increased 


FIG.  87.— Diagram  intended  to  give  an  idea  of  the  aggregate  sectional  diameter  of 
the  different  parts  of  the  vascular  system.  A,  arteries;  C,  capillaries;  V^  veins. 
(After  Schofield.) 

aggregate  capacity  of  the  arterial  branches  until  the  capillary 
region  is  reached.  Here  there  is  a  sudden  expansion  to  a 
tube  approximately  two  feet  in  diameter.  There  is  now  a 
rapid  and  then  a  gradual  reduction  in  size  until  the  tube  rep- 
resenting the  venae  cavae  has  a  diameter  of  two  inches.  Just 
as  water  forced  in  at  a  narrow  end  of  this  tube  would  flow 
quickly  there,  slowly  at  the  widest  part,  and  more  quickly 
again  where  it  passed  from  the  other  narrow  end,  so  the  blood 
flows  rapidly  in  the  aorta  and  the  venae  cavae,*  and  slowly  in 
*  A  good  illustration  taken  from  physical  geography  is  afforded  by 


HO  PULSE  IN  CAPILLARIES  AND   WINS.  i&9 

the  capillaries,  which,  though  thousands  of  times  smaller  than 
the  great  arteries  and  veins,  are  millions  of  times  more  nu- 
merous. 

Why  there  is  no  Pulse  in  the  Capillaries  and  Veins. — 
The  disappearance  of  the  pulse  in  the  arterioles  has  two 
causes,  (i)  the  elasticity  of  the  arteries  and  (2)  the  resist- 
ance offered  to  its  flow  by  friction  in  the  smaller  vessels. 

On  account  of  this  friction  the  larger  arteries  have  diffi- 
culty in  sending  blood  through  them ;  it  therefore  accumu- 
lates in  the  aorta  and  its  large  branches  and  stretches  their 
elastic  walls.  The  stretched  arteries  press  constantly  on  the 
blood  within,  and  keep  squeezing  it  through  the  arterioles 
into  the  capillaries,  both  during  systole  and  diastole.  The 
heart,  in  fact,  keeps  the  big  elastic  arteries  over-distended 
with  blood,  since  before  they  have  had  time  to  lose  their 
grip  on  the  blood  within,  another  systole  occurs  and  fills  them 
up  tight  again.  As  the  arteries  are  thus  always  stretched  and 
always  pressing  on  the  blood,  the  capillaries  receive  a  steady 
supply  and  the  flow  through  them  is  uniform.  This  even 
capillary  flow  passes  on  a  steady  blood  stream  to  the  veins.* 

the  Lake  of  Geneva,  in  Switzerland.  This  is  supplied  at  one  end  by  a 
river  which  derives  its  water  from  the  melting  glaciers  of  some  of  the 
Alps.  From  its  other  end  the  water  is  carried  off  by  the  river  Rhone. 
In  the  comparatively  narrow  inflowing  and  outflowing  rivers  the  current 
is  rapid  ;  in  the  wide  bed  of  the  lake  it  is  much  slower. 

*  "Every  inch  of  the  arterial  system  may,  in  fact,  be  considered  as 
converting  a  small  fraction  of  the  heart's  jerk  into  a  steady  pressure, 
and  when  all  these  fractions  are  summed  up  together  in  the  total  length 
of  the  arterial  system  no  trace  of  the  jerk  is  left.  As  the  effect  of  each 
systole  becomes  diminished  in  the  smaller  vessels  by  the  causes  above 
mentioned,  that  of  this  constant  pressure  becomes  more  obvious,  and 
gives  rise  to  a  steady  passage  of  the  fluid  from  the  arteries  towards  the 
veins.  In  this  way,  in  fact,  the  arteries  perform  the  same  functions  as 
the  air-reservoir  of  a  fire-engine,  which  converts  the  jerking  impulse 
given  by  the  pumps  into  the  steady  flow  of  the  delivery  hose." — 
Huxley, 


190  THE  HUM  AM  BODY. 

The  Object  of  having  no  Pulse  in  the  Capillaries  is  to 

diminish  the  danger  of  their  rupture.  As  we  have  seen,  liq- 
uid has  to  ooze  through  their  walls  to  nourish  the  organs  of 
the  body,  and  wastes  from  the  organs  must  get  to  the  blood 
that  they  may  be  carried  off.  Their  walls  have  therefore  to 
be  very  thin,  and  if  the  blood  were  sent  into  them  in  sudden 
jets  at  each  beat  of  the  heart,  they  would  run  much  risk  of 
being  torn. 

The  Muscles  of  the  Arteries. — The  arteries  have  rings  of 
plain  muscular  fibre  in  their  walls ;  when  these  contract  they 
narrow  the  artery,  and  when  they  relax  they  allow  it  to  widen 
under  the  pressure  of  the  blood  in  its  interior.  The  vessel 
then  carries  more  blood  to  the  capillaries  of  the  organ  which 
it  supplies.  Slushing  is  due  to  a  relaxation  of  the  muscular 
layer  of  the  arteries  of  the  lace  and  neck,  allowing  more  blood 
to  flow  to  the  skin. 

Why  the  Arteries  have  Muscles. — The  amount  of  blood 
in  the  body  is  not  sufficient  to  allow  a  full  stream  of  blood 
through  all  its  organs  at  one  time.  The  muscular  fibres  con- 
trolling the  diameter  of  the  arteries  are  used  to  regulate  the 
blood  flow  in  such  a  manner  that  parts  hard  at  work  shall  get 
an  abundant  supply,  and  parts  at  rest  shall  get  just  enough  to 
keep  them  nourished.  Usually  when  one  set  of  organs  is  at 
work  and  its  arteries  dilated,  others  are  at  rest  and  their  ar- 
teries contracted :  for  example,  when  the  brain  is  at  work,  its 
vessels  are  dilated  and  often  the  whole  head  flushed ;  when 
the  muscles  are  exercised,  a  great  portion  of  the  blood  of  the 
body  is  carried  off  to  them;  during  digestion,  the  vessels  of 
the  alimentary  tract  are  dilated  and  absorb  a  large  share  of 
blood. 

This  control  of  the  amount  of  blood  which  any  organ  re- 
ceives is  accomplished  by  nerve  control  through  the  branches 


EXPOSURE   TO  COLD.  19 1 

of  the  sympathetic  system  upon  the  muscle  fibres  in  the  walls 
of  the  arterioles.  These  branches  are  called  vaso-motor  nerves 
and  the  control  is  called  vaso-motor  action.  Contraction  of 
the  arteriole  walls  is  vaso-constriction,  and  relaxation  of  walls 
vaso-dilatation.  Vaso-motor  action  makes  it  possible  to  give 
any  organ  the  amount  of  blood  it  needs  at  any  time  without 
calling  upon  the  heart  for  extra  work. 

We  can  therefore  understand  how  hard  thought  or  violent 
exercise  soon  after  a  meal,  by  diverting  the  blood  from  the 
abdominal  organs,  is  apt  to  produce  an  attack  of  indigestion. 
Young  persons  whose  organs  have  a  superabundance  of  energy, 
which  enables  them  to  work  under  unfavorable  conditions, 
are  less  apt  to  suffer  in  such  ways  than  their  elders.  One  sees 
boys  running  about  after  eating,  when  older  people  feel  a 
desire  to  sit  quiet  or  even  to  sleep. 

Exposure  to  Cold. — Prolonged  exposure  of  the  surface  to 
cold  is  very  apt  to  be  followed  by  a  catarrhal  condition  of  the 
mucous  membranes  of  the  nose,  throat,  lungs,  or  intestines 
(diarrhoea).  Summer  diarrhoea  is  more  often  due  to  a  chill 
of  the  surface  than  to  the  fruits  eaten.  The  best  preventive 
is  to  wear,  when  exposed  to  sudden  changes  of  temperature,  a 
woollen  garment*  over  the  trunk  of  the  body ;  cotton  and 
linen  permit  any  change  in  the  external  temperature  to  act 
almost  at  once  upon  the  skin.  After  an  unavoidable  exposure 
to  cold  or  wet,  the  thing  to  be  done  is  of  course  to  maintain 
the  cutaneous  circulation ;  movement  should  be  persisted  in, 

*  In  tropical  countries,  it  is  customary  for  soldiers  to  wear  a  flannel 
band  over  the  abdomen,  in  addition  to  other  clothing,  to  prevent  chill 
and  consequent  diarrhoea.  This  has  come  to  be  known  as  a  cholera  belt, 
since  it  has  been  credited  with  considerable  influence  in  reducing  the 
frequency  of  severe  attacks  of  diarrhoea,  which  is  one  of  the  most  easily 
recognized  symptoms  of  cholera. 


192  THE  HUMAN  BODY. 

and  a  thick  dry  outer  covering  put  on  until  warm  and  dry 
underclothing  can  be  obtained. 

In  healthy  persons,  a  temporary  exposure  to  cold,  as  a 
plunge  in  a  bath,  is  good,  since  in  them  the  sudden  contrac- 
tion of  the  cutaneous  arteries  soon  passes  off,  and  is  succeeded 
by  a  dilatation  causing  a  warm  healthy  glow  on  the  surface. 
If  the  bather  remains  too  long  in  cold  water,  however,  this 
reaction  passes  off  and  is  succeeded  by  a  more  persistent  chil- 
liness of  the  surface,  which  may  last  all  day.  The  bath 
should  therefore  be  left  before  this  occurs ;  but  no  absolute 
time  can  be  stated,  as  the  reaction  is  more  marked  and  lasts 
longer  in  strong  persons  and  in  those  used  to  cold  bathing 
than  in  others. 

.  It  is  undoubtedly  true,  however,  that  many  persons  who 
attempt  to  take  daily  cold  baths  fail  to  get  a  warm  reaction 
and  are  physically  depressed  rather  than  stimulated.  Others 
who  have  a  tendency  to  neuralgia  or  rheumatism  may  have 
these  conditions  aggravated  by  such  exposure  to  cold.  It  is 
much  wiser  for  these  persons  to  take  tepid  or  warm  baths. 


CHAPTER  XVI. 
THE  OBJECT  AND  THE  MECHANICS  OF  RESPIRATION. 

The  Object  of  Respiration. — Blood  is  renewed,  as  far  as 
food  materials  are  concerned,  by  substances  either  directly 
absorbed  by  the  blood  vessels  of  the  alimentary  canal,  or 
taken  up  by  the  lymphatics  of  the  digestive  tract  and  after- 
wards poured  into  the  blood.  In  order  that  energy  may  be 
set  free  (Chap.  VIII),  oxidations  must  occur,  necessitating  a 
constant  supply  of  oxygen.  Waste  substances  are  thus  pro- 
duced, which  are  no  longer  of  use  to  the  body,  but  detrimen- 
tal to  it  if  present  in  large  quantity.  The  most  abundant  of 
these  wastes  is  carbon  dioxide  gas. 

The  function  of  respiration  has  for  its  object  (i)  to  renew 
the  supply  of  oxygen  in  the  blood,  and  (2)  to  get  rid  of  the 
carbon  dioxide  produced  in  the  different  organs. 

The  Respiratory  Apparatus  consists  primarily  of  two  elas- 
tic bags,  the  lungs,  placed  in  a  cavity  with  extensible  walls, 
the  thorax.  They  are  filled  with  air  and  communicate  by  air 
passages  with  the  surrounding  atmosphere.  In  the  walls  of 
the  lungs  the  capillary  blood  vessels  form  a  very  close  net- 
work. Through  their  walls  the  blood  receives  oxygen  from 
the  air  and  gives  in  return  carbon  dioxide.  The  air  in  the 
lungs  consequently  needs  renewal,  since  otherwise  it  would 
soon  have  no  oxygen  to  give  to  the  blood,  and  would  become 


194  THE  HUMAN  BODY. 

so  loaded  with  carbon  dioxide  that  it  could  no  longer  receive 
it  from  the  blood.  This  renewal  is  effected  by  a  system 
of  muscles,  bones,  and  cartilages  which  co-operate  to  bring 
about  that  alternating  expansion  and  contraction  of  the  chest 
which  we  call  breathing.  When  the  chest  contracts,  air 
poorer  in  oxygen  and  richer  in  carbon  dioxide  is  expelled 
from  the  lungs ;  when  it  expands,  fresh  air,  rich  in  oxygen, 
and  containing  hardly  any  carbon  dioxide,  is  taken  into  them. 

The  respiratory  organs  are  (i)  the  lungs ;  (2)  the  air  pas- 
sages ;  (3)  the  vessels  of  the  pulmonary  circulation,  including 
the  pulmonary  artery  bringing  the  blood  to  the  lungs,  the 
pulmonary  capillaries  carrying  it  through  them,  and  the  pul- 
monary veins  conveying  it  from  them ;  (4)  the  muscles, 
bones,  and  cartilages  concerned  in  producing  the  breathing 
movements.  * 

The  Air  Passages. — Air  reaches  the  pharynx  through  the 
nose  or  mouth  (Fig.  i).  On  the  ventral  side  of  the  pharynx 
(Fig.  46)  is  an  aperture  through  which  it  passes  into  the 
larynx  or  voice-box  (a,  Fig.  88),  which  lies  in  the  upper 
part  of  the  neck.  From  the  larynx  air  passes  on  through  the 
windpipe  or  trachea,  which  enters  the  chest,  and  in  the  upper 
part  divides  into  a  right  and  a  left  bronchus.  Each  bronchus 
enters  a  lung,  and  divides  in  it  into  a  vast  number  of  very  small 
tubes,  called  the  bronchial  tubes.  The  last  and  smallest  bron- 
chial tubes  (a,  Fig.  89)  open  into  subdivided  elastic  sacs 
(3,  c)  with  pouched  walls. 

Structure  of  the  Trachea  and  its  Branches. — The  trachea, 
bronchi,  and  bronchial  tubes  are  lined  by  mucous  membrane, 
outside  of  which  is  a  supporting  stratum  composed  of  connec- 

*To  these  should  be  added  (5)  the  nerve  centres  and  nerves  which  con- 
trol the  muscles  of  respiration,  and  which  will  be  subsequently  con- 
sidered (see  Chap.  XX). 


THE  AIR  PASSAGES. 


195 


tive  and  plain  muscular  tissues.  Their  walls  also  contain 
incomplete  rings  of  cartilage  which  keep  them  open.  Below 
the  larynx  the  stiff  windpipe  passing  down  to  the  top  of  the 
chest  may  readily  be  felt  in  thin  persons. 

The  Cilia  of  the  Air  Passages. — The  mucous  membrane 


FIG.  88. 

FIG.  88.— The  lungs  and  air  passages  seen  from  the  front.  On  the  left  of  the  figure 
the  pulmonary  tissue  has  been  dissected  away  to  show  the  ramifications  of  the  bron- 
chial tubes,  a,  larynx  ;  b,  trachea  ;  d,  right  bronchus.  The  left  bronchus  is  seen  en- 
tering the  root  of  its  lung. 

FIG.  89. — A  small  bronchial  tube,  a,  dividing  into  its  terminal  branches,  c  \  these 
have  pouched  or  sacculated  walls  and  end  in  the  sacculated  alveoli,  b. 

of  the  trachea  and  its  branches,  except  the  smallest,  has  a  layer 
of  ciliated  cells  on  its  surface.  Each  of  these  cells  has  on 
its  end  turned  towards  the  cavity  of  the  tube  a  tuft  of  from 
twenty  to  thirty  slender  threads  which  are  in  constant  motion  ; 
they  lash  forcibly  toward  the  throat,  move  gently  back  again, 
and  then  once  more  violently  toward  the  outlet  of  the  air  pas- 
sage. These  moving  threads  are  called  cilia.  Swaying  in  the 


196 


THE  HUMAN  BODY. 


mucus  secreted  by  the  membrane  which  they  line,  they  sweep 

it  on  to  the  larynx,  where  it  is  coughed  up. 

Imagine  a  man  rowing  in  a  boat  at  anchor.     The  sweep  of 

the  oars  will  drive  the  water  back  and  not  the  boat  forward. 
So  these  little  oars,  the  cilia,  anchored  on 
the  mucous  membrane,  drive  on  the  secre- 
tion which  bathes  its  surface. 

Bronchitis,  or  "  a  cold  on  the  chest," 
is  an  inflammation  of  the  membrane  lining 
the  bronchial  tubes,  in  consequence  of 
which  it  swells,  and  its  secretion  is  changed 


FIG.  90. 


FIG.  91. 


FIG.  90. — The   trachea,  front.    £,  hyoid  bone;  tt1 ',  thyroid  cartilage;  r,  cricoid;    #, 
epiglottis;  tr,  trachea;  b  and  b' ',  bronchi. 
FIG.  91. — Ciliated  cells  from  the  epithelium. 

in  quantity  and  character.  The  swelling  and  secretion  tend 
to  close  the  tubes  and  interfere  with  the  free  passage  of  air  in 
breathing. 

The  Lungs  consist  of  the  bronchial  tubes  and  their  terminal 
dilatations,  together  with  blood  vessels,  lymphatics,  and 
nerves,  all  bound  firmly  together  by  elastic  tissue.  The  ex- 
pansions called  air  sacs  or  alveoli,  at  the  end  of  each  final 
branch  (Figs.  92  and  93),  are  relatively  very  large,  and 
their  surface  is  still  further  increased  by  the  pouches  which 
project  from  them.  Their  walls  are  highly  elastic,  and  con- 
tain a  close  network  of  capillary  blood  vessels,  supplied  by  the 
pulmonary  artery  and  emptying  into  the  pulmonary  veins. 


THE  LUNGS. 


197 


Through  the  extremely  thin  lining  of  the  air  sac,  and'  the 
thin  wall  of  the  capillaries  im- 
bedded in  it,  oxygen  is  absorbed 
by  the  blood  from  the  air  in 
the  air  sac  and  carbon  dioxide 
given  up  to  it.  It  has  been 
calculated  that  if  the  walls  of 
the  air  cells  were  spread  out  flat 
and  placed  side  by  side  they 
would  cover  an  area  of  2600 
square  feet.  This  great  sur- 
face, therefore,  represents  the 
area  of  the  body  by  which 
oxygen  is  received  and  car- 


FIG.    91. — Two    alveoli   of   the    lung 


,  , .        .,  .  rt-  j   opening   into    its   central   cavity;  <r,  ter- 

DOn       dlOXlde      given       Ott,     and  minal  branches  of  bronchial  tube. 

accounts   for   the    rapidity  with  which  the    exchange    takes 

place. 

The  Pleurae. — The  exterior   of  each  lung,  except  where 

its  bronchus 
and  blood  ves- 
sels enter  it,  is 
covered  by  a 
thin  elastic  ser- 
ous membrane, 
the  pleura  (Fig. 
2),  which  close- 
ly resembles  the 
peritoneum. 


also    lines    the 


FIG.   93. — Diagram   of  expansion  of  end   of  bronchial  tube    '"PUi'c 
in to  air  sacs.    B,  bronchial  tube;  LB,  bronchiole;  A^  entrance 
chamber;    /,    central    cavity    (infundibulum);     C,  C,    alv 
whose  walls  are  covered  with  capillaries. 

inside  of  the  chest.      Its  surface  in  health  is  kept  moist  by 
a  small  quantity  of  lymph.    In  consequence  of  its  smoothness 


198 


THE  HUMAN  BODY. 


and  moisture,  the  lungs  glide  over  the  chest  wall  during  the 
breathing  movements  with  but  little  friction. 

Pleurisy  is  inflammation  of  the  pleura.     In  its  early  stages 


FIG.    94. — Section  of  lung  with  distended  blood  vessels,  highly  magnified,    c,  c,  par- 
titions between  alveoli;  £,  small  artery  giving  off  capillaries  to  alveoli. 

it  is  usually  associated  with  sharp  pain  on  drawing  the  breath. 
Later  on  a  large  quantity  of  lymph  is  often  poured  out  by  the 
inflamed  pleura,  taking  up  space  which  should  be  occupied  by 
the  lung. 

The  Elasticity  of  the  Lungs. — The  lungs  are  as  elastic  as 
a  thin  rubber  bag.  If  we  tie  a  tube  tightly  into  a  bronchus 
and  blow  in  air  the  lung  will  dilate,  but  as  soon  as  we  cease 
blowing  and  leave  the  tube  open,  it  will  shrink  up  again.  Yet 
in  the  chest  the  lungs  always  remain  so  expanded  as  com- 
pletely to  fill  all  the  space  left  for  them  by  the  heart  and 
other  structures  contained  in  the  thorax. 

Inspiration  and  Expiration. — The  process  of  taking  air 


QUANTITY  OF  AIR  BREATHED. 


199 


into  the  lungs  is  known  as  inspiration,  that  of  expelling  it  as 
expiration.  On  the  average,  fifteen  to  eighteen  inspirations 
and  expirations  occur  in  each  minute.  We  therefore  breathe 
in  and  out  about  once  for  every  four  beats  of  the  heart. 

Maximum  inspiration., 


Complentental  air  — 


Ordinary  inspiration 

TIDAL  AIR- 
Ordinary  expiration -- 


Supplemental  air  -- 

Maximum  expiration  - 

Residual  air  - 


Vital  capacity 


Capacity  of  equilibrium 


FIG.  95. — Amounts  of  air  contained  by  the  lungs  in  various  phases  of  ordinary  and 
of  forced  respiration. 


respiration 

Quantity  of  Air  Breathed. — During  ordinary  quiet  res- 
piration, we  inspire  and  expire  about  30  cubic  inches,  or 
about  one  pint,  of  air  ;  this  is  called  the  tidal  air.  After  an 
expiration  of  this  amount,  we  can  still  expire  by  effort  about 
100  cubic  inches  of  air  ;  this  is  called  the  supplemental  air. 
There  still  remains  in  the  lungs  about  100  cubic  inches  of  air 
which  cannot  be  expelled  with  the  most  violent  effort ;  this  is 
the  residual  air.  When  breathing  quietly,  it  is  possible,  after 
an  inspiration  of  the  ordinary  30  cubic  inches  of  air,  to  in- 
spire an  additional  120  cubic  inches  ;  this  is  the  complemental 
air.  Jhe  total  amount  of  air  that  can  be  expired  after  the 
deepest  inspiration  possible  is  called  the  vital  capacity.  This 
varies  in  different  individuals  and  depends  largely  on  the 
movability  of  the  chest  wall. 


200  THE  HUMAN  BODY. 

The  Structure  of  the  Thorax. — The  thorax  is  a  conical 
cavity  with  a  supporting  skeleton  (Fig.  96)  formed  by  the 


FIG.  96 — The  skeleton  of  the  thorax,     a,  £-,  vertebral  column  ;  6,  first  rib  ;  <r,  clavi- 
cle ;  d,  third  rib  ;  z,  glenoid  fossa. 

dorsal  vertebrae  behind,  the  breast  bone  in  front,  and  the  ribs 
and  rib  cartilages  on  the  sides.  Between  and  over  these  lie 
muscles,  and  the  whole  is  covered  air-tight  by  the  skin  outside 
and  the  pleurae  (p.  197)  inside.  Above,  it  is  closed  by  the 
muscles  and  other  organs  of  the  neck ;  below  by  a  movable 
bottom,  the  diaphragm.  The  air-tight  chamber  thus  enclosed 
can  be  enlarged  in  all  three  diameters,  but  especially  in  the 
vertical,  and  in  the  dorso-ventral  (running  from  the  spinal  col- 
umn to  the  breast  bone). 

The  Vertical  Enlargement  of  the  Thorax  is  brought 
about  by  the  contraction  of  the  diaphragm  (Fig.  97),  a  thin 
sheet  of  muscle,  with  a  fibrous  membrane  in  its  centre  serving 


VERTICAL  ENLARGEMENT  OF  THE   THORAX.       201 

as  a  tendon.  In  rest  the  diaphragm  is  dome-shaped,  its  con- 
cavity being  turned  towards  the  abdomen.  From  the  tendon 
on  the  crown  of  the  dome,  striped  muscular  fibres  radiate, 
downward  and  outward,  in  all  directions,  and  are  fixed  by 
their  outer  ends  to  the  six  lawer  ribs,  the  breast  bone,  and 
the  vertebral  column.  In  inspiration  the  muscular  fibres,  by 
shortening,  flatten  the  dome  of  the  diaphragm  and  enlarge  the 


FIG.  97. — The  lower  half  of  the  thorax,  with   four  lumbar  vertebrae,  showing  the 
diaphragm  from  above,     i,  2,  3,  central  tendon  ;  4,  5,  muscular  part. 

thoracic  cavity  by  adding  space  to  its  widest  part  (Fig.  98). 
Since  the  abdominal  cavity  is  surrounded  by  bony  and  dense 
muscular  walls,  except  in  front  where  they  are  thin  and  elastic, 
the  downward  movement  of  the  diaphragm  manifests  itself 
as  an  outward  movement  of  the  front  abdominal  wall. 


202 


THE  HUMAN  BODY. 


Tr 


Si 


A  B 

FIG.  98. — Diagram  to  show  the  changes  in  the  sternum,  diaphragm,  and  abdominal 
wall  in  respiration.  A ,  inspiration  ;  B,  expiration  ;  Tr,  trachea  ;  St,  sternum  ;  D, 
diaphragm  ;  A 6,  abdominal  wall.  The  shaded  part  is  to  indicate  the  stationary  air. 

The   Dor  so- Ventral   Enlargement  of  the  Thorax. — The 

ribs  slope  downward  (  Fig.  15)  from  the 
vertebral  column  to  the  breast  bone,  the 
slope  being  most  marked  in  the  lower 
ones.  During  inspiration  the  breast 
bone  and  the  sternal  ends  of  the  ribs  at- 
tached to  it  are  raised  by  muscles  which 
pull  on  them,  thus  increasing  the  dis- 
tance between  the  sternum  and  the  ver- 
tebral column.  That  this  must  be  so 

.      —Diagram    illustrating      . 

the  dorso  ventral  increase  in  the  will  readily  be  seen  by  examining  the 

diameter    of   the   thorax     when 

the  ribs  are  raised.  diagram   Fig.  99,  where  ab  represents 

the  vertebral  column,  c  and  d  two  ribs,  and  st  the  sterum. 


EXPIRATION.  203 

The  continuous  lines  represent  the  natural  position  of  the 
ribs  at  rest  in  expiration,  and  the  dotted  lines  the  position  in 
inspiration.  It  is  clear  that  when  their  lower  ends  are  raised  so 
as  to  make  the  bars  lie  in  a  more  nearly  horizontal  plane,  the 
sternum  is  pushed  away  from  the  spine,  and  the  extent  of  the 
chest  cavity  between  backbone  and  breast  bone  is  increased. 

Inspiration  requires  a  good  deal  of  muscular  effort.  When 
the  diaphragm  contracts  and  flattens  its  dome,  it  has  to  push 
down  the  abdominal  viscera  on  its  under  side,  and  to  press 
out  the  front  wall  of  the  abdomen  to  make  room  for  them. 
The  ribs,  shoulders,  and  breast  bone  have  also  to  be  lifted  up 
and  the  elasticity  of  the  lungs  overcome. 

Expiration. — In  ordinary  expiration,  on  the  contrary,  no 
muscular  effort  is  required.  As  soon  as  the  muscles  which 
have  raised  the  ribs  and  sternum  relax,  these  bones  return  by 
their  weight  and  the  elasticity  of  the  rib  cartilages  to  their 
former  unconstrained  position.  The  elastic  abdominal  wall 
presses  the  abdominal  viscera  against  the  under  side  of  the 
diaphragm  and  pushes  it  up  again,  as  soon  as  its  muscular 
fibres  cease  contracting.  In  this  way  the  chest  cavity  is 
restored  to  its  original  capacity,  and  the  air  is  sent  out  of  the 
lungs  rather  by  the  elasticity  and  weight  of  the  parts  which 
were  stretched  and  raised  in  inspiration  than  by  any  special 
expiratory  effort. 

When,  however,  an  expiration  is  violent,  as  during  a  sneeze 
or  a  fit  of  coughing,  the  abdominal  muscles  act  as  special 
expiratory  muscles  by  pulling  down  the  ribs  and  pressing 
up  the  diaphragm. 

The  Respiratory  Sounds. — The  entry  and  exit  of  air  are 
accompanied  by  respiratory  sounds  or  murmurs,  which  can  be 
heard  on  applying  the  ear  to  the  chest  wall.  These  sounds 
are  characteristic  over  the  trachea,  the  larger  bronchial  tubes, 


204  THE  HUMAN  BODY. 

and  portions  of  lung  from  which  large  bronchial  tubes  are 
absent.  They  are  variously  modified  in  pulmonary  affections, 
and  hence  the  value  of  auscultation  of  the  lungs  in  assisting 
the  physician  to  form  a  diagnosis. 

Why  the  Lungs  fill  with  Air  may  be  best  understood  by 
considering  a  pair  of  bellows,  as  shown  in  Fig.  100.  A  thin- 
walled  rubber  bag  (£)  is  fitted  loosely  inside  the  bellows  and 

connected  with  the  outside 
^^^^v  "        air  only  through  its  nozzle 


(c).  It  is  possible  to  fill 
the  rubber  bag  either  by 
blowing  air  in  through  the 

FIG.  ioo. — Diagram  to  illustrate  the  entry  of  ,  ,  •          i/u 

air  to   the  lungs  when   the  thoracic  cavity  en-  nOZZlC,   Or    by  Opening   me 

bellows.    When  the  rubber 

bag  is  filled  with  air,  it  is  possible  to  empty  it  either  by 
closing  the  bellows  or  by  releasing  the  handles  and  allow- 
ing the  weight  of  the  bellows  and  the  elasticity  of  the  bag 
to  force  the  air  out.  Whenever  the  cavity  of  the  bellows  is 
made  larger,  air  enters  the  rubber  bag ;  when  made  smaller, 
air  passes  out  from  the  bag.  When  the  bellows  are  being 
opened,  air  enters  the  cavity ;  since  it  is  impossible  to  pull 
air,  this  inward  movement  means  that  air  is  being  pushed 
in.  When  the  bellows  are  being  closed  the  outward  move- 
ment of  air  indicates  similarly  that  there  is  a  force  behind  it 
pushing  it  out.* 

*  It  must  be  remembered  that  we  are  at  the  bottom  of  a  sea  of  air  and 
that  this  sea  is  pressing  on  all  exposed  surfaces  with  a  force  equal  to 
about  15  Ibs.  to  the  square  inch  of  surface,  but  as  it  presses  equally  on 
all  sides  of  objects,  the  pressures  in  opposite  directions  neutralize  each 
other  and  we  do  not  notice  their  presence.  As,  for  example,  when  we 
have  a  piece  of  thin  sheet  rubber,  it  is  perfectly  flaccid.  If,  however, 
we  diminish  the  pressure  upon  one  side  by  putting  the  rubber  over  the 
mouth  and  inhaling,  the  pressure  upon  the  other  side,  though  unchanged, 
is  relatively  greater  and  pushes  the  membrane  in. 


THE  NERVOUS   CONTROL   OF  RESPIRATION.        205 

It  is  thus  apparent  that  so  long  as  air  cannot  enter  between 
the  walls  of  the  rubber  bag  and  the  bellows,  the  rubber  bag 
will  follow  the  movements  of  the  bellows  and  be  emptied  only 
when  the  bellows  are  closed.  The  chest  walls  correspond 
to  the  bellows  and  the  lungs  to  the  inner  rubber  bag.  We 
thus  see  why  the  lungs  cannot  completely  empty  themselves 
during  life,  since  the  chest  wall  is  not  sufficiently  flexible  to 
close  down  upon  them  so  far  as  to  obliterate  the  cavity.  If, 
however,  the  chest  wall  becomes  punctured,  as  by  a  wound, 
connecting  the  chest  cavity  with  the  external  air,  the  external 
air  pressure,  no  longer  withheld  from  the  lung's  surface  by 
the  chest  wall,  presses  upon  it  and  neutralizes  the  pressure 
of  the  air  within  the  lung  which  has  kept  it  expanded ;  the 
lung's  elasticity  then  causes  it  to  collapse  to  a  small  flaccid 
mass. 

The  Nervous  Control  of  Respiration. — The  respiratory 
movements  are  produced  by  contractions  of  muscles  and  are 
controlled  by  the  action  of  nerves.  It  has  been  found  that 
the  nervous  impulses  which  give  rise  to  the  respiratory  move- 
ments are  controlled  in  part  by  a  nervous  centre  in  the  spinal 
bulb,  called  the  respiratory  centre.  Its  activity  seems  to  de- 
pend upon  the  condition  of  the  blood ;  when  the  blood  is 
poor  in  oxygen  and  rich  in  carbon  dioxide  and  other  waste 
matters,  this  centre,  as  also  the  heart  centre,  becomes  active 
and  produces  more  rapid  and  deeper  contractions  of  the  re- 
spiratory muscles;  when  the  blood  is  rich  in  oxygen  and  poor 
in  wastes,  the  centre  is  more  quiescent.  During  vigorous 
exercise,  oxygen  is  used  up  rapidly  from  the  blood  and  the 
respiratory  centre  is  kept  in  a  state  of  greater  activity.  Dur- 
ing sleep,  oxygen  is  used  up  more  slowly  and  the  respiratory 
movements  are  less  frequent. 

Hygienic  Remarks. — Since  the  diaphragm  when  it  con- 


206 


THE  HUMAN  BODY. 


tracts  pushes  down  the  abdominal  viscera  lying  against  its 
under  side,  these  have  to  make  room  for  themselves  by  push- 
ing out  the  soft  front  of  the  abdomen,  which  accordingly  pro- 
trudes when  the  diaphragm  descends.  Hence  breathing  by 
the  diaphragm  is  indicated  on  the  exterior  by  movements  of 


FIG.  101. — Torso  of  the  Statue 
known  as  Venus  of  Melos. 


FIG.  102. — New  York 
Fashion,  1898. 


the  abdomen  (Fig.  98)  and  is  often  called  "abdominal 
respiration,"  as  distinguished  from  breathing  by  the  ribs, 
called  "  costal  "  or  "  chest  breathing."  As  a  rule,  men  and 
children  use  the  ribs  less  than  adult  women.  Since  abdomen 
and  chest  alternately  expand  and  contract  in  healthy  breath- 
ing, anything  which  impedes  their  free  movement  is  to  be 
avoided.  The  tight  lacing  which  is  still  indulged  in  by  those 
who  think  a  distorted  form  beautiful,  seriously  impedes  one 
of  the  most  important  functions  of  the  body,  and  leads  not 


HYGIENIC  REMARKS.  207 

only  to  shortness  of  breath  and  an  incapacity  for  muscular 
exertion,  but  in  many  cases  to  actual  deformity  or  disease. 
The  abdominal  organs  are  compressed  and  forced  downward, 
and  as  a  result  their  attachments  are  stretched  and  their 
functions  impeded.  In  extreme  cases  of  tight  lacing  some 
organs  are  often  directly  injured ;  for  example,  weals  of 
fibrous  tissue  are  found  developed  on  the  liver  from  the  con- 
stant pressure  of  the  lower  ribs  forced  against  it. 


CHAPTER  XVII. 
THE  CHEMISTRY  OF  RESPIRATION  AND  VENTILATION. 

The  Quantity  of  Air  breathed  daily.— After  an  ordinary 
expiration  the  chest  cavity  is  by  no  means  completely  col- 
lapsed, as  the  lungs  still  contain  about  200  cubic  inches  of 
air.  In  the  next  inspiration  30  more  cubic  inches  are  taken 
in,  at  the  following  expiration  about  the  same  amount  is  sent 
out,  and  so  on  throughout  the  day.  During  quiet  breathing 
the  quantity  of  air  in  the  lungs  varies,  therefore,  with  each 
inspiration  and  expiration  between  230  and  200  cubic  inches. 
At  each  inspiration  something  over  a  pint  of  fresh  air  is  taken 
in,  and  at  each  expiration  about  the  same  amount  of  vitiated 
air  is  expelled.  As  each  of  us  breathes  at  least  fifteen  times  a 
minute,  we  thus  use  each  minute  15  X  30  —  450  cubic  inches 
(15^  pints)  of  air.  In  an  hour  the  quantity  is  450  X  60  = 
27,000  cubic  inches  (930  pints),  and  in  twenty-four  hours 
27,000  X  24  =  648,000  cubic  inches  (22,320  pints)  of  air, 
which  weighs  about  28.7  Ibs.  We  have  next  to  see  what  it 
is  that  happens  to  this  vast  quantity  of  air  breathed  daily  by 
each  one  of  us;  what  we  have  taken  out  of  it,  and  what  we 
have  given  off  to  it. 

The  Changes  produced  in  Air  by  being  once  breathed. — 
These  are  fourfold — changes  in  temperature,  moisture,  volume, 
and  in  its  chemical  composition. 

Changes  in  Temperature. — The  air  taken  into  the  lungs 
is  nearly  always  cooler  than  that  expired,  which  has  a  tem- 

208 


CHANGES  IN  MOISTURE.  209 

perature  of  about  36°  C.  (97°  F.).  The  temperature  of  a  room 
is  usually  about  21°  C.  (70°  F. ).  The  warmer  the  inspired 
air,  the  less  the  heat  which  is  lost  by  the  body  in  the  breath- 
ing process. 

Changes  in  Moisture. — Inspired  air  always  contains  more 
or  less  water  vapor,  but  is  rarely  saturated — that  is,  rarely 
contains  all  it  can  take  up  without  showing  it  as  mist. 
The  warmer  air  is,  the  water  vapor  it  requires  to  saturate  it. 
The  expired  air  is  nearly  saturated  at  the  temperature  at 
which  it  leaves  the  body.  This  is  shown  by  the  moisture 
deposited  when  it  is  cooled,  as  on  a  mirror,  or  in  the  clouds 
formed  by  the  breath  on  a  frosty  day.  We  therefore  con- 
clude that  air  when  breathed  gains  water  vapor  and  carries 
it  off  from  the  lungs.  The  quantity  of  water  thus  removed 
from  the  body  is  about  nine  ounces  each  twenty-four  hours. 

Changes  in  Volume. — If  the  expired  air  is  measured  as  it 
leaves  the  body,  its  bulk  will  be  found  greater  than  that  of 
the  inspired  air,  since  it  not  only  has  water  vapor  added  to  it, 
but  is  expanded  in  consequence  of  its  higher  temperature.  If, 
however,  it  is  dried  and  reduced  to  the  same  temperature  as 
the  inspired  air,  its  volume  will  be  found  diminished,  since  it 
has  lost  5.4  volumes  of  oxygen  for  every  4.3  volumes  of  car- 
bon dioxide  which  it  has  gained. 

Chemical  Changes. — The  most  important  changes  brought 
about  in  the  breathed  air  are  those  in  its  chemical  composi- 
tion. Pure  air  when  completely  dried  consists  in  100  parts 
of— 

By  Volume.          By  Weight. 
Oxygen 20.8  23 

Nitrogen 79.2  77 

When  breathed  once,  such  air  gains  rather  more  than  4 
volumes  in  100  of  carbon  dioxide,  and  loses  rather  more  than 


210  THE  HUMAN  BODY. 

5  of  oxygen.      More  accurately,  100  volumes  of  expired  air, 

when  dried,  consist  of—- 
Oxygen   15.4 

Nitrogen 79.2 

Carbon  dioxide 4.3 

The  expired  air  also  contains  volatile  organic  substances  in 
quantities  too  minute  for  chemical  analysis,  but  readily  de- 
tected by  the  nose  upon  coming  into  a  close  room  in  which 
a  number  of  persons  have  been  collected. 

The  Quantity  of  Oxygen  taken  up  by  the  Lungs  in  a 
Day. — We  have  already  seen  that  the  quantity  of  air  breathed 
in  a  day  is  648,000  cubic  inches.  This  loses  5.4  per  cent  of 
oxygen  or  35,000  cubic  inches,  weighing  12,818  grains  (i-J- 
Ibs. ).  The  body  therefore  gains  this  amount  of  oxygen 
through  the  lungs  daily. 

The  Amount  of  Carbon  Dioxide  passed  Out  from  the 
Lungs  in  a  Day  is  4. 3  per  cent  of  the  total  bulk  of  the  air 
breathed,  or  27,864  cubic  inches;  it  weighs  14,105  grains  or 
about  2  Ibs. 

We  thus  find  that  though  each  breath  seems  in  itself  a  very 
little  thing,  the  total  amount  of  matter  received  into  and 
passed  out  of  the  body  through  the  lungs  every  day  of  our 
lives  is  considerable.  In  a  year  each  adult  breathes  about 
10,000  Ibs.  of  air;  from  it  he  takes  657  Ibs.  of  oxygen,  and  to 
it  he  gives  off  730  Ibs.  of  carbon  dioxide. 

Ventilation. — Since  at  each  breath  some  oxygen  is  taken 
from  the  air  and  some  carbon  dioxide  given  to  it,  were  the 
atmosphere  around  a  living  man  not  renewed  he  would  at 
last  be  unable  to  get  from  the  air  the  oxygen  he  required ;  he 
would  die  of  oxygen  starvation  or  be  suffocated,  as  such  a 
mode  of  death  is  called,  as  surely,  though  not  quite  so  fast, 
as  if  he  were  put  under  the  receiver  of  an  air  pump  and  all 


WHEN  BREATHED  AIR  BECOMES   UNWHOLESOME.    211 

the  air  around  him  removed.  Hence  the  necessity  of  ventila- 
tion to  supply  fresh  air  in  place  of  that  breathed.  Clearly 
the  amount  of  fresh  air  requisite  must  be  determined  by  the 
number  of  persons  collected  in  a  room.  Moreover,  since 
gas  and  lamps  use  oxygen  and  give  out  carbon  dioxide,  cal- 
culation must  be  made  for  them  in  arranging  for  the  ventila- 
tion of  a  building  in  which  they  are  to  be  used. 

When  Breathed  Air  becomes  unwholesome. — The  evil 
results  of  insufficient  air  supply  are  not  ordinarily  directly 
due  to  a  lack  of  oxygen,  for  the  blood  flowing  through  the 
lungs  can  take  the  necessary  amount  of  oxygen  from  air  con- 
taining as  little  as  fifteen  or  even  ten  per  cent.  The  head- 
ache and  drowsiness  which  result  from  sitting  in  badly  venti- 
lated rooms,  and  the  lack  of  energy  and  general  ill-health 
which  accompany  permanent  living  in  such  conditions,  are 
dependent  on  a  slow  poisoning  of  the  body  by  the  reabsorp- 
tion  of  matters  eliminated  from  the  lungs  in  previous  respi- 
rations. What  these  are  is  not  accurately  known ;  they 
doubtless  .belong  to  those  volatile  bodies  mentioned  above  as 
carried  off  in  small  quantities  in  each  breath,  since  observa- 
tion shows  that  the  air  becomes  injurious  long  before  the 
reduction  of  oxygen  and  the  increase  of  carbon  dioxide  are 
sufficient  to  do  any  harm.  Breathing  air  which  contains 
one  or  two  per  cent  of  carbon  dioxide  produced  by  ordin- 
ary chemical  methods  does  no  injury,  but  the  breathing  of 
air  containing  one  per  cent  of  carbon  dioxide  produced  by 
respiration  is  decidedly  injurious,  because  of  the  organic 
materials  sent  out  from  the  lungs  at  the  same  time. 

The  percentage  of  carbon  dioxide  in  the  air  may  be  readily 
measured,  whereas  the  more  dangerous  organic  substances  con- 
tained in  expired  air  cannot  be.  These  poisonous  materials, 
however,  always  bear  practically  the  same  relation  to  the 


212  THE  HUMAN  BODY. 

amount  of  carbon  dioxide ;  hence  if  carbon  dioxide  is  esti- 
mated, the  badness  of  the  air,  due  to  the  poisonous  factors, 
may  be  inferred.  It  must  be  remembered,  however,  that 
this  applies  to  the  carbon  dioxide  produced  by  respiration, 
and  not  to  that  produced  by  the  burning  of  gas  or  lamps  ; 
hence  in  rooms  lighted  by  these  means  allowance  must  be 
made,  after  determining  the  amount  of  carbon  dioxide,  for 
that  which  has  been  produced  through  their  agency.  When 
a  very  large  amount  of  carbon  dioxide  is  present  the  air  can- 
not be  safely  respired,  as,  for  example,  at  the  bottom  of  wells 
or  in  brewing  vats.  This  is  due  to  two  factors,  the  absence 
of  oxygen  and  the  presence  of  an  overwhelming  amount  of 
carbon  dioxide. 

The  Quantity  of  Fresh  Air  which  should  be  allowed  for 
each  Person  in  a  Room. — A  man  at  rest  expires  air  contain- 
ing 4$  of  carbon  dioxide,  amounting  in  one  hour  to  about 
-|  cubic  foot.  It  is  agreed  by  hygienists  that  2  parts  of 
respiratory  carbon  dioxide  in  10,000  parts  of  air  are  all  that 
are  permissible  for  respiration.  Hence  air  must  be  introduced 
into  an  occupied  room  in  sufficient  amount  to  reduce  the  re- 
spiratory impurity  of  4$  or  400  parts  in  10,000  to  2  parts; 
therefore  there  must  be  added  to  each  breath  200  parts  of 
fresh  air,  or  3000  cubic  feet  of  air  per  hour  for  each  indi- 
vidual. 

Many  experiments  have  shown  that  there  should  be  an 
allowance  of  about  600  cubic  feet  of  space  for  each  man  in 
the  room.  This  permits  the  requisite  change  of  air  without 
drafts,  and  insures  a  chance  for  the  thorough  mixing  of  ex- 
pired air  with  the  air  of  the  room  so  that  it  will  not  be  re- 
breathed  before  mixing. 

The  nose  of  a  person  entering  a  room  from  the  outside  air 
has  been  found  to  be  an  excellent  test  of  the  purity  of  the  air, 


HOW  TO   VENTILATE. 


213 


and  any  odor  or  sense  of  closeness  detected  in  this  way  sug- 
gests that  the  air  contains  too  much  impurity  to  be  breathed 
with  safety.  The  accompanying  table  shows  the  relation 
between  the  determinations  made  by  the  sense  of  smell  and 
the  chemical  analysis  of  the  amount  of  carbon  dioxide  due  to 
respiratory  impurity  present. 

RELATIONJOF  ORGANIC  MATTER  TO   CARBON  DIOXIDE,   DETER- 
MINED BY  ODOR. 


Condition  of  the  air  of  an  occupied 
room  as  determined  by  the  nose. 


Corresponding  parts  of  CO2  in 
10,000  vols.  of  air  due  to 
respiratory  impurity 

Total  parts  of  CO2  in  10,000 
vols.  of  air  ( =  -j-  4  parts  at- 
mospheric CO2) 


tfk 


«'£  * 

•H 

o.y  sj 


8  II  * 

•§SSa 


8 


6.5 


10.5 


13 


How  to  Ventilate.  —  Ventilation  does  not  necessarily 
mean  draughts  of  cold  air,  as  is  too  often  supposed.  In 
warming  by  indirect  radiation,  as  by  furnace  or  steam  pipes  in 
the  basement,  proper  ventilation  may  readily  be  secured  by 
arranging  openings  connected  with  a  chimney,  by  which  the 
impure  air  may  pass  out  to  make  room  for  the  fresh  warm  air 
to  enter.  Since  the  fresh  air  is  the  warmest  air  of  the  room 
it  goes  immediately  to  the  ceiling  and  will  pass  out  through 
any  openings  it  finds  there.  Hence  all  outlets  should  be  at 
the  floor  level  and  the  inlets  for  warm  air  at  the  ceiling.  An 
open  fire  in  a  room  will  always  keep  up  a  current  of  air 
through  it,  and  is  one  of  the  most  wholesome,  though  not 
most  economical,  methods  of  warming  an  apartment. 

Ordinary  stoves  in  a  room  contribute  little  to  the  vencila- 
tion,  for  they  take  only  a  small  amount  of  air  out  of  the  room 
through  the  chimney  and  bring  in  as  leakage  around  doors 


214  THE  HUMAN  BODY. 

and  windows  only  as  much  as  they  take  out ;  hence  if  these 
rooms  are  occupied  the  air  becomes  quickly  impure.  Some 
stoves  are  provided  with  jackets  inside  of  which  fresh  air  may 
be  admitted  from  outside.  If  there  is  no  such  provision,  it 
is  possible  to  fasten  a  board  three  or  four  inches  wide,  to  fit 
under  the  lower  sash  of  a  window.  Fresh  air  then  enters  by 
the  opening  between  the  two  sashes  at  the  middle  of  the 
window  and  diffuses  through  the  room,  usually  without  draft. 
This  window  should  be  opened  on  the  windward  side  of  the 
room  so  the  air  will  surely  enter.  The  window  on  the  oppo- 
site side  of  the  room  may  be  opened  at  the  bottom  to  allow 
the  foul  air  to  pass  out.  In  this  way  the  change  of  air  in  the 
room  may  be  made  continuous.  Since,  fortunately,  few  doors 
and  windows  fit  quite  tight,  fresh  air  gets  into  closed  rooms 
in  tolerable  abundance  for  one  or  two  occupants. 

Changes  undergone  by  the  Blood  in  the  Lungs. — These 
are  the  exact  reverse  of  those  exhibited  by  the  breathed  air 
— what  the  air  gains  the  blood  loses,  and  vice  versa.  The 
blood  loses  heat,  water,  and  carbon  dioxide,  and  gains 
oxygen.  These  gains  and  losses  are  accompanied  by  a  change 
of  color  from  the  dark  purple  which  the  blood  exhibits  in  the 
pulmonary  artery,  to  the  bright  scarlet  of  the  oxyhaemoglobin 
in  the  pulmonary  veins. 


CHAPTER   XVIII. 
THE    KIDNEYS   AND    THE   SKIN. 

General  Arrangement  of  the  Nitrogen-excreting  Organs. 

—These  organs  are  ( i )  the  kidneys,  the  glands  which  secrete 
the  urine ;  ( 2 )  the  ureters  or  ducts  of  the  kidneys,  which 
carry  the  secretion  to  (3)  the  urinary  bladder,  a  reservoir  in 
which  it  accumulates  and  from  which  it  is  expelled  from  time 
to  time  through  (4)  the  urethra,  an  exit  tube.  The  general 
arrangement  of  these  parts,  as  seen  from  behind,  is  shown  in 
Fig.  103.  The  kidneys  (R)  lie  at  the  back  of  the  abdominal 
cavity,  opposite  the  upper  lumbar  vertebrae,  one  on  each  side 
of  the  middle  line.  Each  is  a  firm  mass,  with  a  convex  outer 
and  a  concave  inner  border,  and  its  tipper  end  a  little  larger 
than  the  lower.  From  the  abdominal  aorta  (A)  a  renal 
artery  (Ar)  enters  the  inner  border  of  each  kidney,  to  break 
up  within  it  into  finer  branches,  ultimately  ending  in  capil- 
laries. These  unite  to  form  the  renal  veins  ( Vr),  one  of 
which  leaves  each  kidney  and  opens  into  the  inferior  vena 
cava  (  Vc].  From  the  concave  border  of  each  kidney  proceeds 
also  the  ureter  (U),  a  slender  tube  opening  below  into  the 
bladder  (  Vu)  near  its  lower  end.  From  the  bladder  proceeds 
the  urethra  (Ua).  The  channel  of  each  ureter  passes  very 
obliquely  through  the  wall  of  the  bladder;  accordingly  if  the 

215 


2l6 


THE  HUMAN  BODY. 


FIG.  103. — The  renal  organs,  viewed  from  behind.  /?,  right  kidney;  A,  aorta;  Ar 
right  renal  artery;  Vc,  inferior  vena  cava;  Vr,  right  renal  vein;  17,  right  ureter;  Vu, 
bladder;  Ua,  commencement  of  urethra. 


STRUCTURE  OF  THE  KIDNEYS.  217 

pressure  in  the  bladder  rises  above  that  of  the  liquid  in  the 
ureter  the  walls  of  the  oblique  passage  are  pressed  together 
and  it  is  closed.  Usually  the  bladder  (which  contains  mus- 
cular tissue  in  its  walls)  is  relaxed,  and  the  urine  flows  readily 
into  it  from  the  ureters.  Since  the  passage  of  the  urethra  is 
kept  closed  by  elastic  tissue  around  the  upper  end,  the  urine 
accumulates  in  the  bladder.  When  the  bladder  contracts  and 
presses  on  its  contents  the  ureters  are  closed  in  the  way  above 
indicated,  the  elasticity  of  the  fibres  closing  the  urethral 
exit  from  the  bladder  is  overcome,  and  the  liquid  is  forced 
out. 

The  Gross  Structure  of  the  Kidneys. — When  a  section  is 
made  through  a  kidney  from  its  outer  to  its  inner  bordei 
(Fig.  104)  it  is  seen  that  a  deep  fissure,  the  hilus,  leads  into 
it.  In  the  hilus  the  ureter  widens  out  to  form  the  pelvis  of 
the  kidney,  which  breaks  up  into  a  number  of  smaller  divisions, 
the  cups  or  calices.  The  cut  surface  of  the  kidney  proper  is 
seen  to  consist  of  two  distinct  parts,  an  outer  or  cortical  por- 
tion, and  an  inner  or  medullary.  The  medullary  portion  is 
less  red  and  more  glistening,  is  finely  striated  in  a  radial 
direction,  and  does  not  consist  of  one  continuous  mass,  but 
of  a  number  of  conical  portions,  the  pyramids  of  Malpighi 
(2').  Each  of  these  pyramids  is  separated  from  its  neighbors 
by  a  prolongation  (*)  of  the  cortical  substance.  This,  how- 
ever, does  not  reach  to  the  apex  of  the  pyramid,  which  pro- 
jects, as  \he  papilla,  into  a  calyx  of  the  ureter.  At  its  outer 
end  each  pyramid  separates  into  smaller  portions  (2"),  sep- 
arated by  thin  layers  of  cortex  and  gradually  spreading  every- 
where into  it.  The  cortical  substance  is  redder  and  more 
granular-looking  than  the  medullary.  It  forms  everywhere 
the  outer  layer  of  the  organ,  besides  dipping  in  between  the 
pyramids  in  the  manner  above  described. 


2l8 


THE  HUMAN  BODY. 


The  renal  artery  divides  in  the  hilus  into  branches  (5)  which 
run  into  the  kidney  substance  between  the  pyramids,  giving 


FIG.  104. — Section  through  the  right  kidney  from  its  outer  to  its  inner  border,  i, 
cortex  ;  2,  medulla  ;  2',  pyramid  of  Malpighi  ;  2".  pyramid  of  Ferrein  ;  5,  small 
branches  of  the  renal  artery  entering  between  the  pyramids  ;  A,  a  branch  of  the  renal 
artery  ;  C,  the  pelvis  of  the  kidney  ;  £/,  ureter  ;  C,  a  calyx. 

off  a  few  twigs  to  them,  and  end  finally  in  a  much  closer 
vascular  network  in  the  cortex. 

The  Minute  Structure  of  the  Kidneys. — The  kidneys  are 
compound  tubular  glands,  composed  of  branched  microscopic 


THE  RENAL  SECRETION. 


219 


uriniferous  tulules,  lined  by  a  single  layer  of  secreting  cells 
(Fig.  105),  supported  by  connec- 
tive tissue,  and  supplied  with 
blood  vessels,  nerves,  and  lym- 
phatics. Each  of  the  final 
branches  of  each  tubule  ends  in 
a  dilatation  which  contains  a 
knot  of  blood  vessels  (Fig.  106), 
through  whose  walls  water  and 
salts  enter  the  tubule.  As  the 
water  trickles  along  the  tubules, 
their  cells  take  the  urea  from 
the  blood  in  the  capillaries 

FIG.  105.— Diagram  of  a  kidney  glo- 

closely      around      them      merulus  and  the  commencement  of  an 
uriniferous  tubule      a,  afferent  blood 


(Fig.    105).     The  tubules  .unite 
in  the  pyramids  to  form  larger 


vessel    pushing   in   the   wall,  w,  of  a 
Malpighian  capsule  and  ending  in  the 


the  sake   of   distinctness   it  is   repre- 


i  .    ,  ,  .  e  sae   o        sncness          s     ep- 

QUCtS,   Which    pOUr  the    Secretion      sented  as  a   wrapping   for  the  whole 

•     tuft;  in  nature  it  forms  a  close  invest- 

llltO  the    CallCCS    Ol    the  pelVIS    Ol      ment  around  each  vessel  of  glomerulus; 

A  ,  space  in  capsule;  d^  neck  of  capsule; 

the    Ureter,   which    then    COnveyS     ff*  first  convoluted  portion  of  an  urin- 

iferous tubule  ;  0,  granular  epithelial 
it  to  the  bladder.  cells  ;  £,  basement  membrane. 

The  Renal  Secretion  is  a  watery,  acid  solution  of  urea  and 
inorganic  salts.  These  solids  amount  to  4  per  cent  of  the 
total  secretion  and  give  the  solution  an  average  specific  grav- 
ity of  1.022.  The  urine  excreted  in  twenty-four  hours  con- 
tains :  urea,  35  gms.  (i|  oz.)  ;  inorganic  salts  (chiefly  sodium, 
potassium,  ammonia,  calcium,  and  magnesium),  26^  gms. 
(f  oz.)  ;  and  water,  1400  gms.  (3  pints).  . 

The  urea,  which  is  secreted  by  the  kidneys  and  was  formerly 
supposed  to  be  formed  there,  is  made  by  the  liver  as  a  final 
oxidation  of  nitrogenous  materials  which  have  been  turned  into 
the  blood  by  the  tissues.  As  the  chief  organs  for  the  excre- 
tion of  this  nitrogenous  waste,  the  kidneys  are  among  the 


220 


THE  HUMAN  BODY. 


most  important  of  the  body.  Any  defect  in  their  healthy 
activity  leads  to  serious  trouble,  due  to  the  accumulation  of 
nitrogenous  wastes  in  the  body. 

The  Skin,  which  covers  the  whole  exterior  of  the  body, 
consists  everywhere  of  two  distinct  layers,  an  outer,  the  cuticle 


vi  eti 


FIG.  106. — Circulation  in  the  kidney.  «/',  small  branch  of  renal  artery  giving  off  the 
branch  vat  which  enters  glomerulus,  issues  as  ve,  and  then  breaks  up  into  capillaries, 
which  after  surrounding  the  tubule  find  their  way  by  v  into  vi,  branch  of  the  renal 
vein  ;  ;;/,  capillaries  around  tubules  in  parts  of  the  cortical  substance  where  there  are 
no  glomeruli. 


or  epidermis,  *  and  an  inner,  the  dermis.     Hairs  and  nails  are 
excessively  developed  parts  of  the  epidermis. 

The  Epidermis  (Fig.  107)  consists  of  cells,  arranged  in 
many  layers  and  united  by  a  small  amount  of  cementing  sub- 
stance. The  deepest  layer  (d)  is  composed  of  elongated  or 
columnar  cells,  set  with  their  long  axes  perpendicular  to  the 
dermis  beneath.  It  is  succeeded  by  several  strata  of  roundish 
cells  (3),  which  in  the  outer  layers  become  more  and  more 


*  A  blister  is  due  to  the  accumulation  of  liquid  between  layers  of  the 
epidermis. 


THE  EPIDERMIS. 


221 


flattened  in  a  plane  parallel  to  the  surface.     The  outermost 
epidermic    stratum   is    composed    of  many   layers    of  much 


FIG.  107. — A  section  through  the  epidermis,  somewhat  diagrammatic,  highly  mag- 
nified. Below  is  seen  a  papilla  of  the  dermis,  with  its  artery,/,  and  veins,  gg ;  a\,  the 
horny  layer  of  the  epidermis;  b,  the  rete  muscosum  or  Malpighian  layer;  d,  the  layer 
of  columnar  epidermic  cells  in  immediate  contact  with  the  dermis;  h,  the  duct  of  a 
sweat  gland. 

flattened  cells  from  which  the  nuclei,  conspicuous  in  the 
deeper  layers,  have  disappeared.  These  superficial  cells  are 
dead,  and  are  constantly  being  shed  from  the  surface  of  the 


222 


THE  HUM4N  BODY. 


body.  Their  place  is  taken  by  new  cells,  formed  in  the 
deeper  layers,  pushed  up  to  the  sur- 
face and  flattened  in  their  progress. 
The  change  in  the  form  of  the  cells  as 
they  travel  outward  is  accompanied 
by  chemical  changes ;  they  finally 
constitute  a  semi  -  transparent  dry 
horny  stratum  (0),  distinct  from  a 
deeper,  more  opaque,  and  softer  layer 
(b  and  d )  of  the  epidermis. 

The   material  which   is    peeled   off 
the  skin  on  rubbing  it  with  a  rough 

FIG.    108.— Magnified    view 

of  the    epidermis,   showing  towel  after   a  warm  bath,   consists  of 

mouths  of  the  sweat  glands. 

dead  outer  scales  of  the  horny  stratum 
of  the  epidermis. 

Nerves  penetrate  the  deeper  layers  of  the  epidermis,  but 
no  blood  vessels  enter  it.  The  epidermis  is  also  penetrated 
by  the  ducts  of  sweat  glands,  which  have  their  mouths  along 
the  ridges  (Fig.  108),  and  by  the  hairs.  In  dark  races  the 
color  is  due  to  a  pigment  contained  chiefly  in  the  deeper 
cells  of  the  epidermis. 

The  Dermis,  or  True  Skin  (Fig.  109),  consists  of  a  close 
felt-work  of  connective  tissue,  which  becomes  wider  meshed 
below  and  passes  gradually  into  the  subcutaneous  areolar 
tissue.  In  texture  it  is  much  like  damp  raw  cotton,  and 
loosely  attaches  the  skin  to  parts  beneath.  In  tanning,  the 
dermis  is  turned  into  leather,  its  connective  tissue  forming  an 
insoluble  and  tough  compound  with  the  tannin  of  the  oak- 
bark  employed.  Wherever  there  are  hairs  bundles  of  plain 
muscular  tissue  are  found  in  the  dermis ;  it  contains  also  a 
close  network  of  capillary  blood  vessels,  and  numerous  lym- 
phatics and  nerves.  In  shaving,  as  long  as  the  razor  keeps 


THE  PAPILLA  OF  THE  DERMIS. 


223 


in  the  epidermis  there  is  no  bleeding ;   but  a  deeper  cut 
shows  at  once  the  presence  of  blood  vessels  in  the  true  skin. 


EJC.. 


FIG.  iog. — Diagram  to  show  the  structure  of  the  skin.     E.c,  epidermis,  corneous 
part;  E.m,  epidermis,  Malpighian  part;  D.c,  connective  tissue  of  dermis;  /,  papilla; 
7,  sweat  gland,  the  coils  of  the  tube  cut  across  or  lengthwise;  d,  its  duct;  ft  fat;  v, 
'  vessels;  «,  nerve;  t.c,  tactile  corpuscle. 


The  Papillae  of  the  Dermis. — The  outer  surface  of  the 
dermis  is  almost  everywhere  raised  into  minute  elevations, 


224  THE  HUMAN  BODY. 

called  papillce,  on  which  the  epidermis  is  molded,  so  that  its 
deep  side  presents  pits  corresponding  to  the  projections  of 
the  dermis.  In  Fig.  108  are  shown  papillae  of  the  dermis 
containing  a  knot  of  blood-vessels,  supplied  by  small  arte- 
ries and  having  the  blood  carried  off  from  them  by  little 
veins.  Other  papillae  contain  no  capillary  loops,  but,  in- 
stead, special  organs  connected  with  nerve-fibres  (tactile  cor- 
puscles'), and  concerned  in  the  sense  of  touch.  On  the 
palm  of  the  hand  the  dermic  papillae  are  especially  well 


FIG.  no. — Section  of  the  skin,  showing  the  hair  follicles,  sebaceous  glands,  and 
the  muscles  of  the  hair,  a,  epidermis;  6,  dermis;  f,  muscles  of  the  hair  follicLs;  </, 
sebaceous  glands. 

developed,  as  they  are  in  most  parts  where  the  sense  of 
touch  is  acute,  and  are  arranged  in  rows.  The  epidermis 
fills  up  the  hollows  between  the  papillae  of  the  same  row,  but 
dips  down  between  adjacent  rows,  and  thus  produces  the 
finer  epidermic  ridges.*  On  the  thumbs  and  finger  tips, 
these  ridges,  finely  dotted  by  the  mouths  of  the  sweat  ducts, 
assume  more  or  less  definite  patterns.  These  patterns,  which 
are  different  in  each  person,  persist  throughout  life  and  are 
used  for  personal  identification.  The  wrinkles  of  old  per- 
sons are  due  to  the  absorption  of  subcutaneous  fat  and  of 

*  The  more  marked  furrows  on  the  palm,  the  so-called  "lines  of  life" 
of  the  gypsy's  palmistry,  have  a  different  origin. 


HAIRS  AND  NAILS.  225 

other  soft  parts  beneath  the  skin,  which  does  not  shrink  to 
the  same  extent  and  is  therefore  thrown  into  folds. 

Hairs,  longer  or  shorter,  are  found  all  over  the  surface  of 
the  body,  except  in  a  few  regions,  as  the  palms  of  the  hands 
and  the  soles  of  the  feet.  A  hair  is  a  slender  thread  of  epi- 
dermis, developed  on  a  special  dermic  papilla  placed  at  the 
bottom  of  a  depression,  formed  by  a  pitting-in  of  the  dermis. 
The  depression  is  known  as  the  hair  follicle.  The  part  of 
the  hair  buried  in  the  follicle  is  called  its  root,  and  is  suc- 
ceeded by  a  stem,  which  (in  uncut  hairs)  tapers  off  to  a  point. 
Each  hair  is  made  up  of  a  number  of  epidermic  cells, 
arranged  together  to  form  a  fibre.* 

Nails. — A  nail  is  a  part  of  the  epidermis,  with  its  horny 
stratum  greatly  developed.  The  back  part  of  the  nail  fits 
into  a  furrow  of  the  dermis,  and  is  called  its  root.  The  visible 
part  consists  of  a  body,  attached  to  the  dermis  beneath  (which 
forms  the  bed  of  the  nail),  and  of  &  free  edge.  Near  the  root 
is  a  little  area,  whiter  than  the  rest  of  the  nail,  called  the 
lunula.  The  whiteness  is  due  in  part  to  the  greater  opaque- 
ness of  the  nail  there,  and  partly  to  the  less  vascular  character 
of  its  bed,  which  when  seen  through  the  nail  causes  its  pink 
color. 

The  portion  of  the  dermis  on  which  the  nail  is  formed  is 
called  its  matrix.  At  the  root  of  the  nail  is  a  groove,  in  which 
by  the  addition  of  new  cells  the  nail  grows  in  length.  The 
part  of  the  matrix  lying  beneath  the  body  of  the  nail,  called 
its  bed,  is  highly  vascular.  New  cells  formed  on  its  bed  and 
added  to  its  under  surface  cause  the  nail  to  increase  in  thick- 
ness, as  it  is  pushed  forward  by  the  new  growth  at  its  root. 

*  The  hairs  of  different  races  often  present  characteristic  differences. 
The  white  races  have  cylindrical  hair,  whereas  negroes  have  flattened  or 
ribbon-like  hair,  hence  its  tendency  to  curl. 


226 


THE  HUMAN  BODY. 


The  free  end  of  a  nail  is  therefore  its  thickest  part.  If  a 
nail  is  ' '  cast ' '  in  consequence  of  an  injury,  or  torn  off,  a 
new  one  is  produced,  provided  the  matrix  is  not  destroyed. 

The  Glands  of  the  Skin  are  of  two  kinds,  sweat  and  oil 
glands. 

The  Sweat  Glands  (Figs.  1 08  and  in)  are  microscopic 
tubes  which  reach  from  the  surface  of  the  skin  to  the  subcu- 
taneous areolar  tissue ;  there  the  tube  often  branches,  and  is 
coiled  up  into  a  little  knot,  intertwined 
with  blood  capillaries.  These  glands  are 
found  all  over  the  skin,  but  are  most 
abundant  on  the  palms  of  the  hands,  the 
soles  of  the  feet,  and  the  brow.  Alto- 
gether, there  are  about  two  and  a  half 
millions  of  them. 

The  perspiration  or  sweat  poured  out  by 
these    glands    is    a    transparent    colorless 
liquid,  with  a  peculiar  odor,  varying  in 
different  races,  and  in  different  regions  of 
the    body.       Its     quantity   in    twenty-four 
hours   is   subject   to  great  variations,   but 
*J  usually  lies  between   700  and  2000  grams 
le  (or  25   and   71  ounces).      The  amount  is 

coils  of  the  gland  proper,   .     ,,  ,  .     ,      ,         ,  -. . 

imbedded  in  the  subcu-  influenced  mainly  by  the  surrounding  tem- 

taneous  fat,  are  seen  be- 
low the  dermis.  perature,  being  greater  when  this  is  high  ; 

but  it  is  also  increased  by  other  conditions  tending  to  raise 
the  temperature  of  the  body,  as  muscular  exercise.*  The 
*  The  secretion  of  perspiration  is  greatly  increased  during  muscular 
exercise  and  is  closely  related  to  the  heat  control  of  the  body,  for  during 
muscular  exercise  much  more  heat  is  produced  in  the  body.  By  the  evap- 
oration of  this  extra  amount  of  perspiration  a  large  share  of  the  heat  is 
removed,  keeping  the  body  temperature  at  the  normal  point  (98°, 4  F.). 
In  fever,  the  sweat  glands  do  not  act ;  as  a  result  the  skin  is  ordinarily 
dry  and  less  heat  is  lost. 


THE  SEBACEOUS  GLANDS.  227 

sweat  may  or  may  not  evaporate  as  fast  as  it  is  secreted ;  in 
the  former  case  it  is  known  as  insensible,  in  the  latter  as  sen- 
sible perspiration.  By  far  the  most  passes  off  in  the  insensible 
form ;  drops  of  sweat  accumulate  only  when  the  secretion  is 
very  profuse,  or  the  surrounding  atmosphere  so  humid  that  it 
does  not  readily  take  up  more  moisture.  The  perspiration 
in  1000  parts  contains  990  of  water  to  10  of  solids.  Among 
the  latter  is,  in  health,  a  little  urea,  some  sodium  chloride, 
and  other  salts.  In  diseased  conditions  of  the  kidneys,  when 
they  are  not  able  to  excrete  all  the  urea  of  the  blood,  it  col- 
lects in  the  blood  and  is  excreted  by  the  skin  in  greater 
amount  than  ordinarily.  By  causing  profuse  perspiration 
under  such  conditions,  a  considerable  amount  of  urea  can  thus 
be  eliminated  from  the  system  to  supplement  the  impaired 
action  of  the  kidneys. 

The  Sebaceous  Glands  usually  open  into  hair  follicles  (Fig. 
no).  They  are  small  compound  racemose  glands  (p.  107). 
Each  presents  a  duct,  opening  near  the  mouth  of  the  hair 
follicle ;  when  followed  back  this  duct  is  found  to  divide  into 
several  branches  which  end  in  globular  expansions,  lined  by 
secreting  cells.  The  mouth  of  the  ducts  discharges  into  the 
hair  follicle. 

The  Sebaceous  Secretion  is  oily  and  semi-fluid.  In  healthy 
persons  it  lubricates  the  hair  and  renders  it  glossy.  It  is  also 
spread  more  or  less  over  all  the  surface  of  the  skin,  and  makes 
it  oily  and  less  permeable  by  water. 

The  Skin  as  a  Sense  Organ. — Besides  its  functions  as  a 
protective  covering  and  an  excretory  organ,  the  skin  is  of  ex. 
treme  importance,  as  being  the  seat  of  the  dermal  senses. 
(Chap.  XXI.) 

Hygiene  of  the  Skin. — The  sebaceous  secretion  and  the 


228  THE  HUMAN  BODY. 

solid  residue  left  by  evaporating  sweat  form  a  film  on  the 
skin.  Hence  the  importance  of  personal  cleanliness.  Ex- 
posed parts  of  the  body  except  the  scalp  should  be 
washed  daily  with  good  soap.  The  entire  body  should  be 
washed  with  warm  water  and  soap  at  least  once  or  twice  a 
week.  If  the  skin  becomes  dry  from  too  frequent  bathing, 
the  oil  should  be  restored  by  use  of  vaseline,  tallow  or  other 
emollient.  No  doubt  many  persons  go  about  in  very  good 
health  with  very  little  washing;  contact  with  the  clothes  and 
other  external  objects  keeps  the  skin  excretions  from  accu- 
mulating to  any  very  great  extent.  But  apart  from  the  duty  of 
personal  cleanliness  imposed  on  every  one  in  daily  intercourse 
with  others,  the  greater  immunity  from  infectious  diseases 
afforded  by  cleanliness  should  be  an  important  inducement. 
Undoubtedly  the  habit  of  washing  the  hands  before  eating  is 
a  most  effective  preventive  measure. 

Bathing. — One  object  of  bathing  is  to  cleanse  the  skin  ; 
another,  -to  strengthen  and  invigorate  the  whole  frame.  For 
some  strong  healthy  persons  a  cold  bath  may  be  the  best ;  but 
in  severe  weather  the  temperature  of  the  water  should  be  raised 
to  15°  C.  (about  60°  F. ),  at  which  it  still  feels  quite  cool  to 
the  surface.  The  first  effect  of  a  cold  bath  is  to  contract  all 
the  skin  vessels  and  make  the  surface  pallid.  This  is  soon 
followed  by  a  reaction,  in  which  the  skin  becomes  red  and 
full  of  blood,  and  a  glow  of  warmth  is  felt.  The  proper  time 
to  come  out  of  the  bath  is  while  this  reaction  lasts,  and  it 
should  be  promoted  by  a  good  rubbing.  If  the  stay  in  the 
cold  water  is  too  prolonged,  the  state  of  reaction  passes  off,  the 
skin  again  becomes  pallid,  and  the  person  feels  cold,  uncom- 
fortable, and  depressed  all  day.  Such  bathing  is  injurious  in- 
stead of  beneficial,  since  it  lowers  instead  of  stimulating  the 
activities  of  the  body.  How  long  one  may  remain  in  cold 


BATHING.  229 

sea  water  with  benefit  depends  greatly  on  the  individual ;  a 
vigorous  man  can  bear  and  set  up  a  healthy  reaction  after  ten 
or  twenty  minutes'  immersion,  whereas  a  feeble  person  may  be 
exhausted  by  one  minute's  exposure.  Of  course,  apart  from 
this,  the  temperature  of  the  water  is  of  great  importance. 
Water  which  feels  cold  to  the  skin  may  vary  within  very  wide 
limits  of  temperature.  The  colder  it  is,  the  shorter  the  time 
which  it  is  wise  to  remain  in  it. 

When  to  Bathe. — It  is  perfectly  safe  to  bathe  when  warm, 
in  spite  of  the  common  belief.  No  one  should  enter  a  cold 
bath  when  feeling  chilly,  when  in  a  depressed  vital  condition, 
or  immediately  after  a  meal.  The  best  time  for  a  long  cold 
bath  is  two  or  three  hours  after  breakfast  or  the  mid-day  meal. 
For  a  brief  daily  dip  there  is  no  better  time  than  on  rising  in 
the  morning. 

Shower  Baths  are  coming  into  general  use  because  of  their 
convenience  and  economy  of  water.  They  may  be  supplied 
with  warm  or  cold  water  and  are  effective  for  both  cleanli- 
ness and  stimulation.  The  cold  shower  is  far  better  than  the 
cold  plunge,  since  it  stimulates  both  by  the  coolness  of  the 
water  and  the  force  with  which  it  conies  against  the  skin.  At 
the  same  time  it  does  not  chill  the  body  nor  lead  to  depres- 
sion by  abstracting  a  large  amount  of  heat. 

Prolonged  Warm  Baths,  except  occasionally  for  purposes 
of  cleanliness,  are  medical  remedies,  and  not  proper  for  daily 
use.  While  promoting  the  tendency  to  perspiration  (often 
important  in  disease),  they  also,  if  often  repeated,  lower  the 
general  vigor  of  the  body. 


CHAPTER   XIX. 
WHY  WE  NEED   A   NERVOUS  SYSTEM.     ITS  ANATOMY. 

The  Harmonious  Co-operation  of  the  Organs  of  the  Body. 

— We  have  already  learned  that  the  body  consists  of  a  vast 
number  of  cells  and  fibres,  combined  to  form  organs,  and  that 
each  kind  of  cell  or  fibre  and  each  organ  has  its  own  peculiar 
structure,  properties,  and  uses.  Except  in  so  far  as  the  blood, 
passing  from  organ  to  organ,  carries  matters  from  one  to 
another,  and  indirectly  enables  each  organ  to  act  upon  the 
rest,  we  have  not  as  yet  studied  the  means  by  which  all  this 
collection  of  organs  is  made  to  work  together,  so  that  each 
shall  not  merely  look  after  itself,  but  regulate  its  activity  in 
relation  to  the  needs  or  dangers  of  the  others. 

That  the  organs  do  co-operate  we  all  know.  When  an 
object  threatens  to  toucli  the  eye,  the  lids  involuntarily  shut. 
When  we  are  using  the  muscles  of  the  legs  vigorously  the 
muscles  of  respiration  hurry  their  action,  that  oxygen  may  be 
conveyed  more  rapidly  to  the  blood  for  the  supply  of  the 
working  leg  muscles,  and  that  the  wastes  produced  by  them 
may  be  quickly  removed.  When  the  sole  of  the  foot  is 
tickled  the  muscles  of  the  thigh  and  leg,  which  are  not 
directly  interfered  with  at  all,  contract  and  jerk  the  foot  away 
from  its  tormentor.  Everywhere  among  the  organs  we  find 
this  co-operation  through  which  our  bodies  are  enabled  to 
continue  alive.  In  ^Esop's  fable  we  are  told  how  the  arms 

230 


A   COLLECTION  OF  LINING   ORGANS.  231 

and  jaws  declined  to  work  any  longer  in  providing  and 
grinding  food  for  the  lazy  stomach,  and  how  they  soon  came 
to  grief  in  consequence.  We  might  extend  the  fable,  and 
tell  how  afterwards  the  stomach  made  up  its  mind  to  digest 
and  absorb  just  as  much  food  as  it  wanted  for  itself,  and  not 
bother  about  supplying  those  cantankerous  arms  and  jaws.  If 
the  stomach  ceased  to  work  for  the  other  parts  they  soon 
would  cease  to  be  able  to  send  food  to  it,  and  so  it  would 
itself  starve  in  turn. 

How  a  Man  differs  from  a  Collection  of  Living  Organs. 
— Throughout  the  body,  heart,  lungs,  stomach,  intestines, 
liver,  muscles,  and  skin,  all  need  one  another's  aid  to  obtain 
food  and  oxygen,  to  remove  wastes,  and  to  avoid  dangers. 
This  co-operation  makes  the  individual  human  being.  A 
mere  mass  of  living  organs,  arranged  together  in  the  form  of 
man's  body,  but  each  acting  without  reference  to  the  rest, 
would  no  more  make  a  man  than  a  mob  of  strong  men  would 
make  an  army.  In  the  mob  the  reckless  courage  of  some,  the 
personal  cowardice  of  others,  the  uncontrolled  ambition  of  a 
few,  would  make  the  crowd  nearly  useless  for  military  pur- 
poses in  spite  of  the  merits  of  its  individual  members.  In 
the  body,  if  the  organs  were  not  disciplined,  controlled,  and 
guided,  so  as  to  work  together  for  the  good  of  the  whole, 
death  would  very  soon  result.  As  a  matter  of  fact  this  is  the 
way  in  which  death  almost  always  does  begin.  The  body  is 
not  built  like  the  deacon's  "  one-hoss  shay,"  to  run  till  every 
part  of  it  gives  out  at  the  same  moment.  Some  important 
organ  ceases  to  do  its  part  properly ;  as  a  consequence  the 
whole  complex  mechanism  is  thrown  out  of  gear,  and  death 
results. 

Co-ordination  means  controlling  and  combining  the  activ- 
ities of  a  number  of  working  units  (whether  men,  organs,  or 


232  THE  HUMAN  BODY. 

machines)  for  the  attainment  of  a  definite  end.  A  promiscuous 
and  undirected  crowd  of  competent  bricklayers,  carpenters, 
hod-carriers,  and  so  forth,  would  be  quite  incompetent  to 
build  a  house.  There  might  be  present  abundant  energy  and 
skill  to  construct  walls,  floors,  and  roof;  but  if  each  man 
worked  for  himself  and  took  no  heed  of  the  rest  the  result 
would  be  an  odd  building,  if  any  at  all.  Hence  the  whole 
work  is  placed  under  the  control  of  a  master  builder,  who 
guides  the  activities  of  individuals  according  to  the  needs 
of  the  moment.  The  healthy  body  may  be  regarded  as  made 
up  of  a  number  of  conscientious  workers,  the  organs,  who  are 
concerned  in  building  it  and  keeping  it  in  repair,  each  one 
acting  so  as  to  co-operate  with  the  rest  for  the  attainment  of 
the  common  end.  The  master  builder  is  represented  by  the 
nervous  system,  which  is  in  communication  with  all  the  other 
organs,  is  influenced  by  the  condition  and  the  needs  of  every 
part  at  each  moment,  and  guides  the  activity  of  all  accordingly. 
Part  of  this  control  is  exercised  consciously,  but  much  more 
is  carried  on  without  our  knowing  anything  about  it. 

Nerve  Trunks  and  Nerve  Centres. — In  dissecting  the  body 
numerous  white  cords  are  found  which  at  first  sight  might  be 
taken  for  tendons.  That  they  are  something  else  soon 
becomes  clear,  since  a  great  many  of  them  have  no  connection 
with  muscles,  and  those  which  have  usually  enter  near  the 
middle  of  the  belly  of  the  muscle,  instead  of  being  fixed  to  its 
ends  as  most  tendons  are.  These  cords  are  nerve  trunks.  If 
followed  from  the  middle  line  of  the  body  (Fig.  112)  each 
will  be  found  to  break  up  into  finer  and  finer  branches,  until 
the  subdivisions  become  too  small  to  be  followed  without  the 
aid  of  a  microscope.  Traced  towards  the  middle  of  the  body 
the  trunk  will,  in  most  cases,  be  found  to  increase  by  the 
union  of  others  with  it,  and  ultimately  to  join  a  much  larger 


DIAGRAM  OF  THE  NERYOUS  SYSTEM.  233 


FIG.  112. — Diagram  illustrating  the  general  arrangement  of  the  nervous  system. 


234  THE  HUMAN  BODY. 

mass  of  different  structure  (spinal  cord,  or  brain).  The  inner 
end  of  a  nerve  is  its  proximal,  and  the  other  its  distal  or 
peripheral  end. 

Nerve  trunks  radiate  all  over  the  body,  branching  and 
becoming  smaller  and  smaller  as  they  proceed  ;  they  end  in 
or  among  the  cells  and  fibres  of  the  various  organs.  The 
general  arrangement  is  shown  in  Fig.  112. 

The  Main  Nerve  Centres. — The  great  majority  of  the 
nerve  trunks  take  their  origin  from  the  brain  and  spinal  cord, 
which  together  form  the  great  cerebro -spinal  centre.  Some 
nerves,  however,  commence  in  rounded  or  oval  masses,  which 
vary  in  size  from  that  of  the  kernel  of  an  almond  down 
to  microscopic  dimensions,  and  which  are  widely  distributed 
in  the  body.  Each  of  these  smaller  centres  is  called  a  gan- 
glion. A  considerable  number  of  the  largest  ganglia  are  united 
directly  to  one  another  by  nerve  trunks,  and  give  off  nerves 
especially  to  blood  vessels  and  to  the  organs  in  the  thoracic 
and  abdominal  cavities.  These  ganglia  and  their  branches 
form  the  sympathetic  nervous  system  (Figs,  i  and  2/9,  as  dis- 
tinguished from  the  cerebro-spinal  nervous  system|  consisting 
of  the  brain  and  spinal  cord  and  the  nerves  proceeding  from 
and  to  them.* 

The  Brain,  Spinal  Cord  and  their  Membranes. — The 
brain  lies  in  the  skull  and  is  continuous  through  the  foramen 
magnum  (Fig.  20)  of  the  occipital  bone  with  the  spinal  cord, 
which  lies  in  the  vertebral  column,  and  should  be  considered 
as  a  part  of  the  brain.  Both  the  brain  and  the  spinal  cord  are 
incompletely  separated  by  grooves  and  fissures  into  similar 
right  and  left  halves.  They  are  very  soft  and  easily  crushed, 

*  The  name  "  sympathetic  nervous  system"  is  largely  a  misnomer, 
since  it  is  a  part  of  the  general  nervous  system  and  works  in  direct  con- 
nection with  it. 


THE  SPINAL   CORD. 


235 


and  are  accordingly  placed  in 
almost  completely  closed  bonj 
cavities,  and  enveloped  by  mem- 
branes which  give  them  support. 
These  membranes  are  three  in 
number.  The  external  covering, 
the  dura  mater,  is  tough,  strong, 
and  composed  of  connective  tissue. 
The  innermost  membrane  in  im- 
mediate contact  with  the  brain 
and  cord,  the  pia  mater,  is  less 
dense  and  tough  than  the  dura 
mater.  A  layer  of  flat  cells  covers 
the  outside  of  the  pia,  and  a  similar 
layer  lines  the  inside  of  the  dura ; 
these  two  layers  form  the  third 
membrane,  the  arachnoid.  In 
the  space  between  the  two  layers 
of  the  arachnoid  is  a  small  quan- 
tity of  watery  cerebro-spinal  liquid. 
The  Spinal  Cord  (Fig.  113)  is 
nearly  cylindrical  in  form,  al- 
though a  little  wider  laterally 
than  dorso-ventrally,  and  taper- 
ing off  at  its  posterior  end.  Its 


FIG.  113. — Diagrammatic  view  from  before 
of  the  spinal  cord  and  medulla  oblongata,  in- 
cluding the  roots  of  the  spinal  and  some  of  the 
cranial  nerves,  and  on  one  side  the  gangliated 
chain  of  the  sympathetic.  The  spinal  nerves  are 
enumerated  in  order  on  the  right  side  of  the 
figure.  Br,  brachial  plexus  ;  CV,  anterior  crural, 
O,  obturator,  and  Sc,  great  sciatic  nerves,  coming 
off  from  lumbo-sacral  plexus  ;  x  ,  x  ,  filum  ter- 
minale  ;  a,  b,  c,  superior,  middle,  and  inferior 
cervical  ganglia  of  the  sympathetic,  the  last 
united  with  the  first  thoracic,  d ;  d ',  the  eleventh 
thoracic  ganglion  ;  /,  the  twelfth  thoracic  (or  first 
lumbar)  ;  below  ss,  the  chain  of  sacral  ganglia. 


FIG.  113. 


236 


THE  HUMAN  BODY. 


average  diameter  is  about  J  inch  and  its  length  1 7  inches. 
It  weighs  i£  ounces.  There  is  no  marked  limit  between  the 
spinal  cord  and  the  brain,  the  one  passing  gradually  into  the 
other.  In  its  course  the  cord  presents  two  expansions,  an 
upper  (Fig.  113),  the  cervical  enlargement,  reaching  from 
the  third  cervical  to  the  first  dorsal  vertebrae,  and  a 
lower  or  lumbar  enlargement,  opposite  the  last  dorsal 
vertebrae. 


6' 


FIG.  114. — Diagrams  of  spinal  cord  and  nerve  roots.  ,  A,  a  small  portion  of  the  cord 
seen  from  the  ventral  side  ;  Z>,  the  same  seen  laterally  ;  C,  a  cross-section  of  the  cord  ; 
D,  the  two  roots  of  a  spinal  nerve  ;  i,  anterior  (ventral)  fissure;  2,  posterior  (dorsal) 
fissure  ;  3,  surface  groove  along  the  line  of  attachment  of  the  anterior  nerve  roots  ;  4, 
line  of  origin  of  the  posterior  roots;  5,  anterior  root  filaments  of  a  spinal  nerve  ; 
6,  posterior  root  filaments  ;  6',  ganglion  of  the  posterior  root ;  7,  7',  the  first  two 
divisions  of  the  nerve  trunk  after  its  formation  by  the  union  of  the  two  roots. 

Running  along  the  middle  line  on  both  the  ventral  and  the 
dorsal  aspects  of  the  cord  are  fissures  which  (C,  Fig.  114) 
nearly  divide  it  into  right  and  left  halves. 

A  transverse  section  (Fig.  115)  shows  that  the  substance  of 


THE  SPIRAL  NERVES.  *3f 

the  cord  is  not  alike  throughout,  but  that  its  white  superficial 
layers  envelop  a  central  gray  substance  containing  nerve  cells 


FIG.  115. — A  thin  transverse  section  of  half  the  spinal  cord  magnified  about  TO  di- 
ameters, i,  anterior  fissure  ;  2,  posterior  fissure;  3,  central  canal  ;  8,  f>ia  mater 
enveloping  the  cord  ;  6,  7,  bands  of  pia  mater  penetrating  the  cord  and  supporting 
its  nerve  elements  ;  9,  a  posterior  root  ;  10,  bundles  of  an  anterior  root ;  a,  £,  r,  d,  e, 
groups  of  nerve  cells  in  the  gray  matter. 

arranged  somewhat  in  the  form  of  a  capital  H.  The  crescent- 
shaped  halves  of  the  gray  matter  are  turned  back  to  back  and 
united  across  the  middle  line  by  the  gray  commissure. 

The  white  portion  of  the  spinal  cord  surrounding  the  cen- 
tral gray  matter  is  composed  almost  entirely  of  nerve  fibres 
with  their  sheaths.  These  pass  up  and  down  the  cord  in  well- 
defined  tracts. 

The  Spinal  Nerves.— Thirty-one  pairs   of  spinal  nerves 


238  THE  HUMAN  BODY, 

join  the  spinal  cord  in  the  neural  canal  of  the  vertebral  col- 
umn, entering  the  canal  through  the  intervertebral  foramina 
(Fig.  113).  Each  divides  in  the  foramen  into  a  dorsal  and 
ventral  portion,  known  respectively  as  the  dorsal  and  ven- 
tral roots  of  the  nerve  (6  and  5,  Fig.  114),  which  are  at- 
tached to  the  sides  of  the  cord.  On  each  dorsal  root  is  a 
spinal  ganglion  (6',  Fig.  114),  placed  where  it  joins  the  ventral 
root  to  make  up  the  common  nerve  trunk.  Immediately  after 
its  formation  by  the  mixture  of  fibres  from  both  roots,  the 
trunk  begins  to  divide  into  branches  for  the  supply  of  some 
region  of  the  body. 

The  Brain  (Fig.  116)  is  far  larger  than  the  spinal  cord  and 
more  complex  in  structure.  It  weighs  on  the  average  about 
50  ounces  in  the  adult.  The  brain  consists  of  three  main 


FIG.  116. — Diagram  illustrating:  the  general  relationships  of  the  parts  of  the  brain. 
A ,  fore-brain  ;  b,  mid-brain;  B,  cerebellum  ;  6",  pons  Varolii  ;  Z>,  medulla  oblon- 
gata  ;  2?,  C,  and  D  together  constitute  the  hind-brain. 

masses,  each  with  subsidiary  parts,  following  one  another  in 
series  from  before  back,  and  respectively  known  as  the  fore- 


THE  BRAIN.  239 

brain,  mid-brain,  and  hind-brain.*  In  man  the  fore -brain  (A), 
weighing  about  44  ounces,  is  much  larger  than  all  the  rest 
put  together  and  overlaps  them.  It  is  formed  chiefly  of  two 
large  convoluted  masses,  separated  from  one  another  by  a 
deep  fissure,  and  known  as  the  cerebral  hemispheres.  The 
great  size  of  these  is  very  characteristic  of  the  human  brain  in 
contrast  to  the  lower  animals.  Beneath  each  cerebral  hemi- 
sphere is  an  olfactory  lobe  (I,  Fig.  118),  inconspicuous  in  man, 
but  in  animals  often  larger  than  the  cerebral  hemispheres,  as  in 
most  fishes.  The  mid-brain  (6)  forms  a  connecting  isthmus 


FIG.  117. — The  brain  from  the  left  side.  Cb,  the  cerebral  hemispheres  forming  the 
main  bulk  of  the  fore-brain  ;  Ct>l,  the  cerebellum  ;  Mo,  the  medulla  oblongata  ;  P,  the 
pons  Varolii  ;  *,  the  fissure  of  Sylvius. 


between  the  two  other  divisions.  The  hind-brain  consists  of 
three  main  parts ;  on  its  dorsal  side  the  cerebellum  (B,  Fig. 
116),  on  the  under  side  the  pons  Varolii  (C,  Fig.  116),  and 

*  The  terms  arise  from  the  relative  positions  of  the  three  hollow  nodules 
in  the  embryonic  central  nervous  tract,  which  later  develop  to  form  these 
portions  of  the  adult  brain. 


240  THE  HUMAN  BODY. 

behind  the  medulla  oblongata  (Z>,  Fig.  116),  which  joins  the 
spinal  cord. 

In  nature  the  main  divisions  of  the  brain  are  not  separated 
as  has  been  represented  in  the  diagram  for  the  sake  of  clear- 
ness, but  lie  close  together  with  the  mid-brain  entirely  covered 
on  its  dorsal  side  (Fig.  117).  Nearly  everywhere  the  surface 
of  the  brain  is  laid  in  folds,  known  as  the  convolutions,  which  are 
deeper  and  more  numerous  in  man  than  in  any  of  the  animals. 

The  brain,  like  the  spinal  cord,  consists  of  gray  and  white 
nervous  matter,  but  somewhat  differently  arranged,  since  in 
addition  to  containing  gray  nerve  matter  in  its  interior,  a 
great  part  of  the  brain's  surface  is  also  covered  with  it.  By 
the  numerous  convolutions  of  the  cerebellum  and  of  the  cere- 
bral hemispheres,  the  surface  over  which  this  gray  substance  is 
spread  is  very  much  increased. 

The  Cranial  Nerves. — Twelve  pairs  of  nerves  leave  the 
skull  cavity  by  apertures  in  its  base,  and  are  known  as  the 
cranial  nerves.  Most  of  them  spring  from  the  under  side  of 
the  brain,  which  is  represented  in  Fig.  118.  The  first  pair, 
or  olfactory  nerves  (I),  are  the  nerves  of  smell ;  they  arise  from 
the  under  sides,  of  the  olfactory  lobes  and  pass  out  through 
the  roof  of  the  nose.  The  second  pair,  or  optic  nerves(II),  are 
the  nerves  of  sight ;  they  spring  from  the  mid-brain,  and, 
under  the  name  of  optic  tracts,  run  down  to  the  under  side  of 
the  fore-brain,  where  they  unite  to  form  the  optic  commissure, 
from  which  an  optic  nerve  proceeds  to  each  eyeball. 

All  the  remaining  cranial  nerves  arise  from  the  hind-brain. 
The  third  pair,  or  motor  nerves  of  the  eye  (III),  are  distributed 
to  three  of  the  muscles  which  move  the  eyeball,  and  also  to 
the  muscle  which  lifts  the  upper  eyelid. 

The  fourth  pair  (IV)  are  quite  small ;  each  goes  to  one 
muscle  of  the  eyeball. 


THE   CRANIAL   NERl/ES. 


241 


The  fifth  pair  or  trigeminals  (V)  resemble  the  spinal  nerves 
in  having  two  roots,  one  of  which  possesses  a  ganglion  (the 
Gasserian  ganglion).  Beyond  the  ganglion  the  two  roots 


in 


ncl 


FIG.  118. — The  base  of  the  brain.  The  cerebral  hemispheres  are  seen  overlapping 
all  the  rest.  /,  olfactory  lobes  ;  //,  optic  tract  passing'  to  the  optic  commissure  from 
which  the  optic  nerves  proceed  ;  ///,  the  third  nerve  or  motor  oculi  ;  IV,  the  fourth 
nerve  or  patheticus ;  V,  the  fifth  nerve  or  trigeminalis ;  VI,  the  si.xth  nerve  or 
abducens ;  VII,  the  seventh  or  facial  nerve  or  portio  dura;  VIII,  the  auditory 
nerve  or  portio  mollis  ;  IX,  the  ninth  or  glosso-pharyngeal  ;  X,  the  tenth  or  pneu- 
mogastric  or  vagus  ;  X I,  the  spinal  accessory  ;  XII,  the  hypoglossal  ;  ncl,  the  first 
cervical  spinal  nerve. 

form  a  common  trunk  which  divides  into  three  main  branches. 
The  first  of  these,  the  ophthalmic,  is  distributed  to  the  muscles 
and  skin  over  the  forehead  and  upper  eyelid,  and  also  gives 
branches  to  the  mucous  membrane  lining  the  nose,  and  to  the 


24*  THE  HUMAN  BODY. 

integument  over  that  organ.  The  second  division,  the  supe- 
rior maxillary  nerve,  gives  branches  to  the  skin  over  the 
temple,  to  the  cheek  between  the  eyebrow  and  the  angle  of 
the  mouth,  to  the  upper  teeth,  and  to  the  mucous  membrane 
of  the  nose,  pharynx,  soft  palate  and  roof  of  the  mouth.  The 
third  division,  the  inferior  maxillary,  is  the  largest  branch  of 
the  trigeminal.  It  is  distributed  to  the  side  of  the  head,  the 
external  ear,  the  lower  lip,  the  lower  part  of  the  face,  the 
mucous  membrane  of  the  mouth,  the  anterior  two  thirds  of 
the  tongue,  the  lower  teeth,  the  salivary  glands,  and  the 
muscles  which  move  the  lower  jaw  in  mastication. 

The  sixth  pair  (VI)  are  distributed  each  to  one  muscle  of 
the  eyeball  on  its  own  side. 

The  seventh  pair,  or  facial  nerves  (VII),  are  distributed 
to  most  of  the  muscles  of  the  face  and  scalp. 

The  eighth  pair ,  or  auditory  nerves  (VIII),  are  the  nerves  of 
hearing,  and  are  distributed  to  the  inner  part  of  the  ear. 

The  ninth  pair,  or  glosso-pharyngeal  nerves  (IX),  are  dis- 
tributed chiefly  to  tongue  and  pharynx. 

The  tenth  pair,  pneumogastric  nerves  or  vagi  (X),  give 
branches  to  the  pharynx,  gullet,  stomach,  larynx,  windpipe, 
lungs,  and  heart.  The  vagi  run  farther  through  the  body 
than  any  other  cranial  nerves. 

The  eleventh  pair,  or  spinal  accessory  nerves  (XI),  do  not 
arise  mainly  from  the  brain,  but  from  the  spinal  cord  by  a 
number  of  roots  attached  to  its  upper  portion,  between  the 
anterior  and  posterior  roots  of  the  proper  spinal  nerves.  Each 
enters  the  skull  cavity  alongside  of  the  spinal  cord,  gets  a  few- 
filaments  from  the  medulla  oblongata,  and  passes  out  by  the 
same  aperture  as  the  glosso-pharyngeal  and  pneumogastric 
nerves.  Outside  the  skull  the  spinal  accessory  divides 
into  two  branches,  one  of  which  joins  the  pneumogastric 


THE  SYMPATHETIC  NERVOUS  SYSTEM.  243 

trunk.  whrle  th*  other  is  distributed  to  muscles  al>out  the 
shoulders. 

The  twelfth  flair,  or  hypoglossal  nerves  (XII),  are  distrib- 
uted mainly  to  the  muscles  of  the  tongue. 

The  Sympathetic  Nervous  System. — The  ganglia  which 
form  the  main  centres  of  the  sympathetic  nervous  system  lie 
in  two  rows  (Fig.  113),  one  on  each  side  of  the  bodies  of 
the  vertebrae.  Each  ganglion  is  united  by  a  nerve  trunk  with 
the  one  anterior  and  the  one  posterior  to  it.  Two  chains  are 
thus  formed  reaching  from  the  base  of  the  skull  to  the  coccyx 
and  lying  in  the  ventral  cavity  (Fig.  2). 

Each  ganglion  is  united  by  short  branches  to  neighboring 
spinal  nerves,  and  near  the  skull  to  various  cranial  nerves  also. 
From  the  ganglia  and  their  uniting  cords  arise  numerous 
trunks,  forming  networks  in  the  thorax  and  abdomen,  from 
which  nerves  are  given  off  to  the  organs  situated  in  those 
cavities.  Many  sympathetic  nerves  finally  end  in  the  walls 
of  the  blood  vessels  of  various  organs.  To  the  naked  eye 
they  are  commonly  grayer  in  color  than  the  cerebro-spinal 
nerves. 

By  means  of  the  junctions  between  the  cranial  and  spinal 
nerves  and  the  sympathetic  system,  the  brain  controls  the 
parts  supplied  by  this  system. 

Nerve  Tissue. — The  microscope  shows  that  the  nervous 
organs  contain  structures  peculiar  to  themselves,  known  as 
nerve  fibres  and  nerve  cells.  The  cells  are  found  only  in  the 
brain,  cord  and  ganglia,  whereas  the  fibres,  of  which  there 
are  two  main  varieties  known  as  the  white  and  the  gray,  are 
found  throughout  the  nervous  system.  The  white  variety 
predominates  in  the  cerebro-spinal  nerves  and  in  the  white 
substance  of  the  brain  and  cord  ;  the  gray,  in  the  sympathetic 
trunks  and  the  gray  portions  of  the  brain  and  cord. 


244 


THE  HUMAN  BODY. 


White  Nerve  Fibres  consist  of  extremely  delicate  threads, 
about  -g-gVo  incn  ^n  diameter,  but  frequently  of  a  length  pro- 
portionally very  great.  If  a  perfectly  fresh  white  nerve  fibre 
is  examined  with  the  microscope  it  presents  the  appearance 
of  a  homogeneous  glassy  thread.  Soon,  however,  it  acquirer 
a  characteristic  double  border  (Fig.  119),  from  the  coagula- 


1) 


E 


FIG.  119. — To  illustrate  the  structure  of  nerve  fibres.  ^4,  nerve  fibre  examined 
fresh:  «,  node.  B,  nerve  fibre  with  axis  cylinder  shaded,  and  medulla  represented 
by  dark  lines :  «.<r,  nucleus  ;  /,  granular  cell  substance  near  the  nucleus.  C,  more 
highly  magnified:  m,  medulla  ;  «,  node.  Z>,  nerve  treated  with  reagents  to  show  the 
axis  cylinder :  n.x,  surrounded  by  medulla,  in.  E,  nerve  treated  with  reagents  to 
show  n.c,  nucleus  with  fine  line  over  it  representing  the  neurilemma,  and  outside  this 
fine  connective  tissue,  c  :  n.c' ,  nucleus  lying  in  the  fine  connective  tissue.  F,  nerve 
fibre  deprived  of  its  neurilemma  showing  medulla  broken  up  into  fragments,  m,  sur- 
rounding the  axis  cylinder,  n.x. 

tion  of  a  portion  of  its  substance,  as  a  result  of  which  three 
layers  are  brought  into  view.  Outside  is  a  thin  transparent 
envelope  called  the  primitive  sheath  or  neurilemma;  inside 


GRAY  NERVE  FIBRES,  245 

this  is  a  fatty  substance,  forming  the  medullary  sheath  (the 
coagulation  of  which  gives  the  fibre  jts  double  border);  in 
the  centre  is  a  core,  the  axis  cylinder,  which  is  the  essential 
part  of  the  fibre,  since  near  its  ending  the  primitive  and 
medullary  sheaths  are  frequently  absent.  At  intervals  of 
about  ^  inch  along  the  fibre  are  found  nuclei.  In  the  course 
of  a  nerve  trunk  its  fibres  rarely  divide ;  when  a  branch  is 
given  off  some  fibres  merely  separate  from  the  rest,  much  as 
a  skein  of  silk  might  be  separated  at  one  end  into  smaller 
bundles  containing  fewer  threads.  The  white  matter  of  the 
spinal  cord,  brain,  and  nerve  trunks  consists  largely  of  med- 
ullated  nerve  fibres,  whereas  the  gray  matter  of  the  cord  and 
brain  consists  largely  of  nerve  cells. 

Gray  Nerve  Fibres  have  no  medullary  sheath,  and  consist 
merely  of  an  axis  cylinder  and  primitive  sheath.  Gray  fibres 
are  especially  abundant  in  the  sympathetic  trunks,  and  are 
the  only  ones  found  in  the  olfactory  nerve. 

Nerve  Cells. — In  the  ganglia  lying  in  the  course  of  nerves 
and  in  the  gray  matter  of  the  spinal  cord  and  the  brain  are 
found  large  nucleated  and  branched  cells  connected  with  the 
nerve  fibres,  and  called  ganglion  or  nerve  cells.  They  differ 
in  size,  shape,  and  number  of  branches,  but  present  fairly 
characteristic  appearances. 

The  cell  substance  is  granular  and  contains  a  large,  round* 
nucleus  with  a  central  spot  called  the  nucleolus.  There  are 
usually  several  branches  which  subdivide  to  form  tree-like 
forms.  One  branch,  however,  does  not  divide,  but  forms 
the  nerve  fibre,  axis  cylinder  or  neuron,  which  finds  its  way 
out  to  other  parts  of  the  nervous  system. 

It  was  formerly  supposed  that  the  nerve  cells  were  con- 
nected with  each  other  by  means  of  their  branches  and  axis 
cylinders,  but  it  has  recently  been  shown  that  each  nerve  cell 


246  THE  HUMAN  BODY. 

with  its  branches  and  axis  cylinder  forms  an  anatomical  unit 
and  that  the  nutrition  of  the  branches  and  axis  cylinder 
depends  entirely  upon  their  connection  with  the  nerve  cell. 


FIG.  120. — A  large  nerve  cell  from  the  ventral  horn  of  the  spinal  cord.  «,  nucleus; 
«',  small  body,  called  the  nucleolus,  inside  the  nucleus  ;  /,  branched  processes  ;  «./, 
unbranched  process  continued  into  the  axis  cylinder  of  a  motor  nerve  fibre. 

If  the  nerve  fibre  becomes  injured,  the  end  of  the  fibre 
beyond  the  point  of  injury  dies  and  is  replaced  by  a  new 
fibre  which  grows  out  from  the  cell. 

The  Structure  of  Nerve  Centres. — The  nerve  cells  repre- 
sent the  active  part  of  the  nervous  tissue.  Since  they  are 
grouped  in  special  localities  of  the  body,  such  as  the  ganglia, 
spinal  cord  and  brain,  these  are  called  nerve  centres.  This  is 
especially  true  of  the  brain  and  spinal  cord,  which  constitute 
the  central  nervous  system.  The  nerve  centres  consist  of 
white  and  gray  nerve  fibres,  of  nerve  cells,  and  of  connec- 
tive tissue  and  blood  vessels,  arranged  together  in  different 
ways  in  different  centres. 


CHAPTER  XX. 

THE  GENERAL  PHYSIOLOGY  OF  THE  NERVOUS  SYSTEM. 

Nature  of  Nervous  Impulse. — A  nervous  impulse  has  so 
little  direct  manifestation  that  it  has  been  impossible  to  de- 
termine its  true  nature.  It  shows  itself  mainly  in  muscular 
contraction,  glandular  activity,  etc.  It  is  transmitted  with 
such  great  rapidity  through  the  nerves  (one  hundred  feet  per 
second)  that  it  is  difficult  to  suppose  that  it  is  a  mechanical 
or  chemical  process;  at  the  same  time  it  is  so  much  slower 
than  an  electric  current  that  it  is  probably  not  at  all  related 
to  it.  It  is  thought  to  be  a  molecular  change  of  some  kind 
passed  along  the  axis  cylinder. 

If  a  nerve  is  cut,  and  an  electric  current  is  sent  through  it, 
the  contraction  of  the  muscle  attached  to  it  shows  that  a  ner- 
vous impulse  has  passed  along  the  nerve.  If  a  drop  of  acid 
or  of  a  strong  salt  solution  is  placed  on  the  end  of  the  nerve, 
the  same  result  is  reached.  Under  natural  conditions,  how- 
ever, nervous  impulses  do  not  arise  in  nerve  fibres,  but  in 
nerve  cells  or  in  special  structures  connected  with  the  ends 
of  nerves,  as  the  sense  organs.  Experiments  have  shown 
that  a  nerve  fibre  merely  conducts  the  nervous  impulse,  but 
has  no  share  in  its  formation  or  modification. 

The  strength  of  the  nervous  impulse  judged  from  a  mechan- 
ical standpoint  is  infinitely  less  than  the  energy  which  is  dis- 
charged in  muscle  or  gland  as  a  result  of  its  action;  it  bears 

247 


248  THE  HUMAN  BODY. 

very  much  the  relation  to  the  muscular  energy  which  the 
force  required  to  pull  the  trigger  of  a  gun  bears  to  that  devel- 
oped by  the  explosion  of  the  powder.  The  discovery  that 
nerve  cells  are  not  continuous  with  each  other  by  means  of 
their  fibres,  but  that  each  cell  and  its  branches,  including  the 
axis  cylinder,  forms  a  distinct  unit,  complicates  the  problem 
of  the  real  nature  of  the  nervous  impulse.  Anatomically 
the  path  from  the  skin  through  the  nerve  trunks  to  the 
spinal  cord  and  thence  up  to  the  cortex  of  the  brain  is  made 
up  of  a  number  of  these  units.  The  impulse  which  travels 
from  the  end  of  the  finger  to  the  cortex  of  the  brain  to  excite 
consciousness  must  either  leap  from  one  unit  to  another  in  this 
chain  in  order  to  bring  its  message  to  consciousness,  or  the 
nervous  impulse  of  one  cell  must  when  transmitted  along  its 
axis  cylinder  (neuron)  be  able  to  stimulate  the  next  cell  to 
discharge  a  similar  impulse  along  its  neuron  until  the  final 
stage  is  reached  and  a  change  in  consciousness  produced.  If 
the  latter  supposition  is  true,  the  cells  act  as  relays,  and  we 
have  what  maybe  called  a  relay  system. 

Nerve  Action. — When  the  large  nerve  trunk  which  passes 
down  the  thigh  is  cut  across,  an  animal  loses  the  power  of 
movement  in  the  muscles  of  the  leg.  It  is  also  unconscious 
of  pinching  or  pricking  of  the  skin  of  the  leg;  in  fact,  it  is 
possible  to  mutilate  its  leg  to  any  extent  without  giving  rise 
to  pain.  If,  however,  the  distal  end  of  the  cut  nerve  is 
pinched  or  an  electric  shock  is  sent  through  it,  the  muscles 
contract.  If  the  proximal  end  of  the  cut  nerve  is  pinched  or 
an  electric  shock  is  sent  through  it,  the  animal  shows  signs  of 
pain. 

The  nerve  trunks  transmit  to  muscles  stimuli  which  cause  them 
to  contract  (motor  stimuli}. 

Sensations  do  not  lie  in  the  exterior  parts  of  the  body. 


NERVE  ACTION. 


249 


Nerve  trunks  transmit  stimuli  which  give  rise  to  sensation,  as, 
for  example,  sensations  of  pain  (sensory  stimuli). 


/ 


FIG.  T2i. — Illustrating  the  functions  of  the  spinal  nerves.    Divided  at  a. — Irritated 
at  i :  pain.     Irritated  at  2  :  muscular  contraction. 

When  the  ventral  nerve  roots  of  spinal  nerves  are  cut,  all 
power  of  motion  is  lost  in  the  muscles  with  which  they  are 
connected.  In  this  case,  however,  the  animal  feels  perfectly 


FIG.  122. — Illustrating  the  functions  of  the  roots  of  the  spinal  nerves,  a,  ventral 
root;  /,  dorsal  root.  Divided  at  a. — Irritated  at  i  :  no  result.  Irritated  at  2  :  con- 
traction of  muscles  supplied  with  fibres  from  the  root.  Divided  at  p. — Irritated  at 
3  :  no  result.  Irritated  at  4  :  pain  produced. 

the  stimulation  of  the  skin  to  which  the  nerve  trunks  are  dis- 
tributed. If  the  distal  ends  of  these  nerves  are  stimulated 
electrically,  it  causes  contraction  of  the  muscles.  When 
the  proximal  ends  are  stimulated  electrically,  there  is  no 
effect. 

The  nerves  which  transmit  the  motor  stimuli  pass  through  the 
ventral  roots  of  the  spinal  nerves. 

Motor  nerves  carry  stimuli  outward  from  the  central  part  of 
the  nervous  system  (efferent  ne,  vet). 


250  THE  HUMAN  BODY. 

When  the  dorsal  roots  are  cut  and  the  anterior  are  in- 
tact, the  power  of  motion  in  the  limb  is  not  affected,  but  all 
sensation  is  lost.  If  the  distal  ends  are  stimulated  electrically 
or  pinched  there  is  no  effect,  but  when  the  proximal  ends  are 
stimulated  pain  is  manifested. 

The  nerves  which  transmit  the  sensory  stimuli  pass  through 
the  dorsal  roots  of  the  spinal  nerves. 

Sensory  nerves  carry  stimuli  from  the  outside  of  the  body 
toward  the  central  part  of  the  nervous  system  (afferent  nerves). 

It  has  also  been  found  that  when  an  animal  has  been  tired 
out,  as  a  bird  by  flying,  the  nerve  cells  in  the  ventral  part 
of  the  gray  matter  of  the  cord,  with  which  the  nerves  of  the 
fatigued  muscles  are  connected,  show  distinct  changes  in  their 
microscopic  structure.  These  changes  have  been  interpreted 
to  mean  fatigue  of  the  nerve  cells.  When  these  cells  are  de- 
stroyed, the  power  of  motion  is  lost  in  the  connected  muscles. 

The  motor  nerve  cells  which  cause  the  contractions  of  the 
muscles  with  which  they  are  connected  by  nerves  lie  in  the  ven- 
tral cornua  of  the  spinal  cord. 

When  the  ganglia  of  the  dorsal  roots  of  the  spinal  nerves 
are  destroyed,  sensation  is  lost  in  the  parts  connected  by 
fibres  with  the  cells  lying  in  the  destroyed  region. 

Sensory  cells  lie  in  the  ganglia  of  the  dorsal  roots  of  the 
spinal  nerves. 

When  the  upper  part  of  the  spinal  cord  is  injured,  all  sen- 
sation and  voluntary  motion  are  lost  in  the  legs  and  lower 
trunk ;  the  individual  becomes  unconscious  of  the  entire  lower 
part  of  his  body.  If  the  sole  of  the  foot  is  then  tickled  with 
a  feather  or  quill,  or  a  hot  object  applied  to  it,  the  foot  is 
jerked  away  by  the  muscles  of  the  leg,  showing  that  the  power 
of  motion  is  in  itself  intact. 

The  motor  nerve  cells  of  the  cord  are  not  capable  of  starting 


NERYE  ACTION. 


251 


voluntary  contractions,  but  depend  upon  stimuli  from  other 
cells. 

They  may  be  stimulated  by  strong  sensory  stimuli  from  the 
periphery  to  produce  protective  movements  (reflex  action). 

The  seat  of  sensation  does  not  lie  in  the  spinal  cord. 

When  the  gray  matter  in  certain  localities  of  the  cortex  of 
the  brain  is  removed,  power  of  voluntary  motion  is  lost  for 
certain  muscles.  When  the  nerve  cells  lying  in  the  same 


Fv 


FIG.  123.— Diagram  of  outer  surface  of  left  cerebral  hemisphere  to  illustrate  the 
localization  of  functions.  The  motor  area  is  shaded  in  vertical  and  transverse  lines  : 
Sy,  fissure  of  Sylvius  ;  an,  angular  gyrus  or  convolution  ;  Ro,  fissure  of  Rolando  ;  Fv, 
frontal  lobe  ;  Pa,  parietal  lobe  ;  Te,  temporal  lobe.  Only  a  very  few  of  the  more  im- 
portant fissures  are  indicated. 

localities  of  the  brain  are  stimulated,  muscular  movements  are 
caused  in  the  group  of  muscles  that  was  paralyzed  by  the  re- 
moval of  the  cells.  The  removal  of  cortical  gray  matter  near 
the  fissure  of  Rolando  (Fig.  123)  in  the  left  side  of  the  brain, 
for  example,  gives  rise  to  paralysis  of  the  right  leg  muscles ; 
the  stimulation  of  cells  in  the  same  region  causes  contraction 
of  the  same  muscles. 


252  THE   HUMAN  BODY. 

The  motor  cells  which  cause  voluntary  muscular  movements 
are  seated  in  the  cortex  of  the  brain. 

Definite  areas  of  the  brain  correspond  to  certain  muscular 
groups,  as  leg,  arm,  and  tongue  (localization  of  functions) . 

The  motor  areas  of  each  side  of  the  brain  correspond  with 
muscular  groups  upon  the  opposite  side  of  the  body.* 

Afferent  Nerves. — All  sensory  nerves  are  afferent  nerves, 
but  not  all  afferent  nerves  are  sensory,  since  many  nerves 
bring  impulses  inward  to  the  central  nervous  system  which 
do  not  result  in  sensation  ;  among  these  are  the  afferent  nerves 
from  the  heart,  muscles,  and  viscera. 

Efferent  Nerves. — Motor  nerve  impulses  have  their  most 
tangible  manifestations  in  muscular  contractions  (musculo- 
motor),  but  these  do  not  constitute  the  most  important  of  the 
outgoing  stimuli  transmitted  by  the  efferent  nerves,  since  they 
are  also  concerned  in  controlling  the  heart  (car dio -motor),  the 
secretion  of  glands  (seer eto -motor),  intestinal  movements  (vis- 
cero-motor),  changes  in  blood  vessels  (vaso-motor) ,  and  cellular 
activity  in  general  (trophic  -\). 

In  addition,  efferent  nerves  have  a  distinctly  different  func- 
tion. The  vagus,  for  example,  tends  to  retard  or  inhibit  the 
action  of  the  heart,  and  the  vaso-dilator  nerves  are  supposed 
to  diminish  the  stimulation  of  the  vaso-constrictors  when  they 
cause  a  dilatation  of  blood  vessels.  This  action  is  called 
inhibition,  and  the  nerves,  inhibitory  nerves.  Since  these  in- 
hibitory results  are  due  to  nervous  stimuli  sent  out  from  the 

*  This  is  true  in  general,  but  it  is  claimed  that  either  side  of  the  brain 
can  control  both  sides  of  the  body,  though  it  does  not  have  to  do  so 
under  normal  conditions. 

•f-  Trophic  nerves  are  those  which  are  supposed  to  stimulate  nutritive 
changes  in  the  cell  itself,  that  is,  to  bring  about  in  the  cell  those  changes 
which  keep  it  in  good  working  order.  The  existence  of  such  nerves  has 
not  been  demonstrated,  but  is  inferred, 


RELATION  BETWEEN  SENSATION  AND  MOTION.    253 

central   nervous  system,    the    nerves  which    carry  them  are 
efferent  nerves. 

Relation  between  Sensation  and  Motion. — When  a  hot 
iron  is  applied  to  the  skin,  muscles  contract  so  as  to  remove 
the  threatened  part  from  danger.  As  we  have  seen,  this  takes 
place  even  when  the  spinal  cord  is  injured,  provided  that  the 
point  of  injury  is  above  the  place  where  lie  the  sensory  and 

Nerve  cells  with  intermingling  branches,  not  continuous  between  cells 


8 


Afferent  Nerve  Fiber 

i  Efferent  Nerve  Fiber 


Sensory < 
Epithelinm 

Muscle 


FIG.  124. — Diagram  of  reflex  arc.    (After  Colton.) 

motor  cells  directly  concerned.  This  movement  is  very  quick, 
taking  only  .06  to  .08  Sec.  Experiments  have  shown  con- 
clusively that  the  nerve  cells  (sensory  and  motor)  concerned 
in  this  action  are  located  in  the  gray  matter  of  the  cord. 
Since  the  motion  immediately  follows  the  stimulation  without 
the  intervention  of  consciousness,  it  is  said  to  be  "reflected  " 
and  the  process  is  called  a  spinal  reflex. 

If  the  irritation  of  the  skin  is  so  slight  that  it  does  not  give 
rise  to  a  reflex  withdrawal,  it  may  excite  consciousness  and 


254  THE  HUMAN  BODY. 

the    consequent    desire    for  withdrawal  on   the   part    of  the 
individual.        Under     these    circumstances    the    least    time 

required    for    the    move- 
Cortex  cerebri    °J^        ^f '  ment    is    much     greater, 

averaging  .15  Sec.,  since 
the  impulse  has  to  be 

transmitted   to  the  brain 
Spinal  bull)  and  cord  3>        ^9 

and  a  much  greater  num- 
ber of  cells  have  to  act. 
This  process  is  known  as  a 
voluntary  reaction. 

Functions  of  the  Spinal 

FIG.  125. — Voluntary  reaction,    i,  epithelium  •  r>__.j         -iir       r, 

2,   afferent  nerve  fibre  ;   3,  spinal  sensory  cell  ;    tOld. We    have     SCCn 

4,  afferent  tract  ;  5,  cortial  sensory  cell;  6,  com-  11                      i             j 

missural  fibre  ;  7,  cortical  motor  cell  ;  8,  efferent  that  the  Spinal  COrd  COn- 
tract  ;  9,  spinal  motor  cell  ;  10,  efferent  nerve 

fibre;  n,  muscle.  taillS  (i)  Cells  which  have 

the  power  of  producing  muscular  contractions,  (2)  cells 
which  receive  sensory  impulses  from  the  nerve  endings, 
as  in  the  skin,  and  (3)  nerve  fibres  which  connect  these 
cells  with  the  periphery  and  with  other  cells  in  the  upper 
part  of  the  spinal  cord  and  the  brain.  Many  experi- 
ments on  animals  with  the  spinal  cord  intact  but  with  the 
brain  destroyed  show  that  they  are  able  to  make  complicated 
reflex  movements  which  are  in  general  of  a  protective  nature. 
As  we  study  the  normal  individual  we  see  that  many  of  the 
sudden  movements  made  are  of  the  nature  of  the  spinal  reflex, 
since  they  are  done  so  quickly  that  the  individual  cannot 
inhibit  them,  as  winking.  We  thus  see  that  the  cord  acts 
(i)  as  a  motor  centre,  either  in  response  to  stimulation  from 
cells  in  the  brain,  or,  reflexly,  in  response  to  sensory  stimuli 
in  the  periphery,  and  (2)  as  a  conductor  of  nervous  impulses 
from  the  periphery  to  the  brain,  and  the  reverse. 

The  motor  and  sensory  fibres  which  pass  up  the  cord  to 


FUNCTION  OF  THE  SPINAL  BULB.  255 

the  brain  cross  from  one  side  to  the  other.  Thus  the  right 
side  of  the  body  is  in  general  controlled  by  the  left  side  of 
the  brain  and  vice  versa.  The  sensory  fibres  cross  shortly 
after  entering  the  cord  in  the  dorsal  root.  The  motor  fibres 
cross  mainly  in  the  upper  part  of  the  cord,  where  they  may 
be  recognized  as  interlacing  bundles.  These  motor  and  sen- 
sory fibres  find  their  way  through  the  length  of  the  spinal 
cord  in  fairly  well  defined  columns  or  tracts  outside  of  the 
gray  matter. 

Functions  of  the  Spinal  Bulb  (Medulla  Oblongata). — The 
spinal  cord  at  its  upper  part,  just  before  its  union  with  the 
brain,  expands  and  opens  out,  exposing  the  gray  matter  on 
its  dorsal  side.  This  expansion  of  the  cord  is  called  the 
spinal  bulb  or  medulla  oblongata.  Experiments  have  shown 
that  nerve  cells  in  the  spinal  bulb  include  among  others  those 
which  have  direct  control  of  the  heart  beat  and  of  respira- 
tion. These  centres  have  been  described  as  automatic,  but 
it  is  probably  not  true  that  they  are  automatic  in  the  sense 
that  they  initiate  the  muscular  contractions  of  the  heart  or 
respiratory  muscles  without  any  stimulus  coming  to  them. 
They  are  doubtless  reflex  centres  and  are  stimulated  from 
without,  probably  by  the  condition  of  the  blood.  When  the 
spinal  bulb  is  injured  death  results  from  the  cessation  of  the 
heart  action  and  of  breathing.  Hence  it  is  one  of  the  vital 
centres  of  the  nervous  system. 

Functions  of  the  Ganglia  of  the  Brain. — In  the  base  of 
the  brain,  covered  over  by  the  cerebral  hemispheres,  lie 
isolated  patches  of  gray  matter  known  as  the  basal  ganglia. 
The  functions  of  these  are  not  well  understood  since  experi- 
mental evidence  is  more  or  less  contradictory,  owing  to  the 
difficulty  of  performing  experiments  without  injuring  adjacent 
nerve  fibres. 


256  THE  HUMAN  BODY. 

Functions  of  the  Cerebrum. — When  the  cerebral  hemi- 
spheres of  a  pigeon  are  destroyed  and  the  rest  of  the  body  is 
in  a  normal  condition,  the  animal  can  still  control  its  muscles 
so  as  to  execute  many  movements,  but  gives  no  sign  of  con- 
sciousness. Left  to  itself  it  will  stand  still  until  it  dies ;  corn 
and  drink  placed  before  it  arouse  in  it  no  idea  of  eating ;  it 
will  die  of  starvation  surrounded  by  food.  Yet  it  can  move 
all  of  its  muscles,  and  if  food  is  placed  in  its  mouth  will  swal- 
low it.  If  its  tail  is  pulled  it  will  walk  forward  •  if  it  is  put 
on  its  back  it  will  get  on  its  feet ;  if  it  is  thrown  into  the  air 
it  will  fly  until  it  strikes  against  something  on  which  it  can 
alight ;  if  its  feathers  are  ruffled  it  will  smooth  them  with  its 
bill. 

The  difference  between  a  pigeon  in  this  state  and  an  un- 
injured pigeon  lies  in  the  absence  of  the  power  of  forming 
ideas  or  of  initiating  movements.  It  has  no  thoughts,  no  ideas, 
no  will.  We  cannot  predict  what  an  uninjured  pigeon  wrill 
do  under  varying  conditions ;  we  can  predict  what  the  pig- 
eon with  no  cerebral  hemispheres  will  do ;  it  is  a  mere  ma- 
chine or  instrument,  which  can  be  played  upon.  In  such  a 
pigeon  the  excitation  of  any  given  sensory  nerve  excites 
reflexly  the  nerve  centres  of  the  spinal  cord  and  brain, 
which  cause  certain  muscles  to  contract,  resulting  in  the 
same  invariable  movement.  The  pigeon  exhibits  no  evi- 
dence of  possessing  consciousness  ;  it  has  no  desires  or  emo- 
tions ;  it  stays  quiet  while  left  to  itself,  and  reacts  reflexly 
when  any  stimulus  is  given  to  it,  and  always  in  an  unvarying 
manner. 

In  human  beings,  accidental  injury  to  parts  of  the  brain 
and  disease  have  made  it  possible  to  study  the  associated 
losses  of  power.  This  evidence  confirms  the  inferences  based 
upon  experiments  on  the  lower  animals,  and  shows  that  in  the 


BRAIN  LOCALIZATION.  257 

human  brain  the  functions  are  distributed  in  much  the  same 
way  as  in  dogs  and  pigeons.  All  actions  directed  by  volun- 
tary attention  thus  find  their  origin  in  the  nerve  cells  of  the 
cerebrum. 

Brain  Localization. — As  we  have  seen,  certain  portions  of 
the  cortex  of  the  cerebrum  are  associated  with  definite  move- 
ments of  the  limbs,  etc.  These  motor  areas  have  been 
mapped  out  with  so  great  clearness  that  in  a  number  of  cases 
of  paralysis  due  to  brain  tumor  the  surgeon  has  confidently 
cut  into  the  brain  in  a  definite  spot  and  located  the  trouble. 
Experiments  show,  however,  that  the  movements  which  are 
caused  by  stimulation  of  the  cells  in  these  areas  are  complex 
movements,  such  as  scratching  or  picking  up  objects,  involv- 
ing a  large  number  of  muscles  which  are  definitely  controlled 
to  accomplish  a  certain  end. 

Since  the  motor  cells  in  the  spinal  cord  act  upon  single 
fibres  of  muscles,  there  are  doubtless  intermediate  motor  cen- 
tres standing  between  the  cells  of  the  cortex  of  the  brain  and 
the  immediate  motor  cells  of  the  cord  which  have  the  power 
of  controlling  large  numbers  of  spinal  motor  cells  and  unify- 
ing their  work. 

This  mechanism  is  somewhat  similar  to  that  existing  in  a 
factory.  The  individual  workmen  correspond  to  the  spinal 
motor  cells ;  the  foremen  who  oversee  the  work  of  these  men 
correspond  to  the  intermediate  cells ;  and  the  superintendent 
who  has  charge  of  the  foremen,  and  hence  of  the  whole  es- 
tablishment, corresponds  to  the  cells  of  the  brain. 

The  centres  of  the  brain  associated  with  the  sense  organs, 
as  seeing  and  hearing,  are  pretty  definitely  localized,  but 
those  which  have  to  do  with  intellectual  processes,  as  mem- 
ory, reasoning,  and  association,  have  not  been  definitely 
localized.  Doubtless  they  have  no  definite  localization,  since 


25 8  THE  HUMAN  BODY. 

each  process  probably  involves  one  phase  of  the  activity  of 
many  groups  of  brain  cells. 

Intercentral  Fibres. — It  is  easy  to  see  that  the  various 
processes  which  thus  call  into  play  large  numbers  of  brain 
cells  necessitate  nerve  fibres  to  connect  the  cells  of  different 
parts  of  the  cortex.  These  fibres  are  called  intercentral  or 
commissural  fibres  and  take  their  paths  between  the  brain 
cells,  without  passing  out  of  the  cranium. 

Functions  of  the  Cerebellum. — When  the  cerebellum  is 
removed  from  animals  they  stand  and  walk  unsteadily,  stag- 
gering and  fluttering  with  many  useless  movements.  The 
muscles  tend  to  contract  in  a  less  purposeful  way  and  with  less 
vigor.  The  manifestations  permit  little  of  definite  inference 
except  this,  that  the  cerebellum  is  concerned  to  some  degree 
with  the  co-ordination  of  muscular  contractions.  It  is  a  large 
organ,  and  it  is  to  be  inferred  that  it  has  important  functions ; 
their  definite  values,  however,  are  not  yet  well  determined. 

Modes  of  Nervous  Reaction. — The  simplest  mode  of  re- 
action is  a  spinal  reflex,  such  as  the  instant  withdrawal  of  the 
hand  upon  coming  into  contact  with  a  hot  stove.  The  re- 
sponse is  immediate,  always  the  same,  preceded  by  no  con- 
ception of  the  movement  to  be  made  and  by  no  conscious 
memory  of  the  means  of  making  it.  The  sensory  stimuli  pass 
up  the  afferent  nerve  to  the  sensory  cells,  which  in  turn  in- 
fluence other  cells  until  finally  certain  motor  cells  are  selected 
and  stimulated  to  send  impulses  down  the  efferent  nerves 
which  result  in  a  complicated  but  co-ordinated  contraction  of 
a  number  of  muscles,  producing  a  protective  movement.  A 
voluntary  reaction  is  more  complicated.  When  a  bright  ball  is 
held  before  a  child,  the  light  waves  enter  the  eye,  are  trans- 
lated in  the  retina  into  nervous  impulses  which  travel  along 
the  afferent  nerves  to  the  optic  sensory  centre  of  the  brain. 


THE   USE  OF  REFLEX  CENTRES.  259 

The  cells  of  this  centre  communicate  with  appropriate  centres 
through  intercentral  tracts  and  a  desire  for  the  ball  results. 
Motor  centres  are  then  stimulated,  beginning  probably  with 
the  arm  group  of  the  cortex  and  ending  with  the  motor  cells 
in  the  spinal  cord.  These  latter  cells,  thus  selected  and  uni- 
fied in  their  action  by  the  higher  motor  centres,  stimulate  the 
muscle  fibres  to  produce  by  their  contractions  the  definite 
movements  which  give  possession  of  the  ball.  This  mode  of 
action  cannot  be  predicted,  involves  consciousness,  and  may 
even  permit  considerable  delay  between  the  stimulation  and 
the  response,  as  in  the  case  of  one  whose  desire  to  visit 
Europe,  aroused  by  books  of  travel,  finds  motor  completion 
only  after  the  lapse  of  years. 

The  line  between  reflex  and  voluntary  reaction  cannot  be 
sharply  drawn  in  ordinary  activity.  Voluntary  reactions  tend 
through  constant  repetition  to  have  reflex  characteristics  in 
that  the  motor  response  follows  directly  upon  the  sensory 
stimuli,  as  in  walking.  The  cells,  at  first  directed  by  con- 
sciousness, have  become  trained  to  do  their  work  without  its 
supervision,  but  doubtless  the  same  motor  cells  are  involved 
as  in  a  corresponding  voluntary  reaction. 

The  Use  of  Reflex  Centres  is  to  relieve  the  thinking  cen- 
tres of  the  vast  amount  of  work  which  would  be  thrown  upon 
them  if  every  action  of  the  body  had  to  be  planned  and  willed 
at  each  moment.  Were  not  the  unconscious  regulating  nerve 
centres  always  at  work  the  mind  would  be  overburdened  by 
the  mass  of  business  which  it  would  have  to  look  after.  No 
time  would  be  left  for  intellectual  development  if  we  had  to 
think  about  and  to  will  each  heart  beat,  each  inspiration  and 
expiration,  and  the  swallowing  of  each  mouthful  of  food. 
Sleep  would  be  impossible,  and  life  as  we  know  it  could  not 
be  maintained. 


260  THE  HUMAN  BODY. 

Habits. — Every  time  a  nerve  cell  acts  in  a  given  way,  it 
becomes  easier  for  it  to  repeat  the  action ;  as  a  result 
many  actions  which  are  at  first  performed  only  with  trouble 
and  thought  are  executed  easily  and  unconsciously.  The  act 
of  walking  is  a  good  instance  ;  each  of  us  in  infancy  learned  to 
walk  with  much  pains  and  care,  thinking  about  each  step.  But 
the  more  we  walked  the  more  the  nervous  system  became 
trained  to  adapt  the  muscular  movement  to  the  guidance  of  the 
nerve  impulses  from  the  sole  of  the  foot.  At  last  the  contact  of 
the  foot  with  the  ground,  stimulating  some  sensory  nerves,  acts 
so  readily  on  the  "  nerve  centres  of  walking  "  that  conscious- 
ness need  take  no  heed  about  it :  we  walk  ahead  while  think- 
ing of  something  else.  Other  instances  will  readily  come 
to  mind,  as  the  difficulty  with  which  we  learned  to  ride,  swim, 
or  skate,  when  obliged  to  think  about  and  will  each  move- 
ment, and  the  ease  with  which  we  do  all  these  after  a  little 
practice.  The  trained  nerve  centres  then  do  all  the  co-ordi- 
nating work  and  consciousness  has  no  more  need  to  trouble 
about  the  matter.  A  habit  simply  means  that  the  unconscious 
parts  of  the  nervous  system  have  been  trained  to  do  certain 
things  under  given  conditions. 

We  thus  find,  in  the  tendency  of  the  nervous  system  to  go 
on  doing  what  it  has  been  trained  to  do,  a  physiological  rea- 
son for  endeavoring  to  form  good  and  to  avoid  bad  habits  of 
every  sort.  Every  thought,  every  action,  leaves  in  the  ner- 
vous system  its  result  for  good  or  ill.  The  more  often  we 
yield  to  temptation  the  stronger  the  effort  required  to  resist 
it,  whereas  every  resistance  of  temptation  helps  to  make  sub- 
sequent resistance  easier. 

Growth  of  the  Brain. — The  nervous  system  in  the  human 
being  grows  more  slowly  than  any  other  part  of  the  body,  for 
while  the  nerve  cells  are  complete  in  number  in  childhood, 


HYGIENE  OF  THE  BRAIN.  261 

yet  their  branches  and  consequently  their  means  of  communi- 
cating with  other  cells  are  not  fully  developed  until  much 
later,  even  as  late  as  the  twenty-fifth  or  thirtieth  year  of  life. 
As  we  have  seen,  the  power  of  the  nervous  system  to  co- 
ordinate the  activities  of  the  body  depends  very  largely  upon 
the  number  and  extent  of  these  branches.  In  this  lies,  in  part, 
the  explanation  of  the  slowness  with  which  the  mental  power 
of  the  child  develops  and  the  fact  that  ripe  judgment,  which  is 
the  final  test  of  nerve  action,  is  found  only  in  the  mature  man 
or  woman.  Much  of  the  precocity  which  is  not  rare  in  child- 
hood is  due  simply  to  an  exceptional  memory,  and  does  not 
mean  real  intellectual  force. 

Hygiene  of  the  Brain. — The  brain,  like  the  muscles,  is 
improved  and  strengthened  by  exercise  and  injured  by  over- 
work or  idleness.  A  man  may  especially  develop  one  set  of 
intellectual  faculties  and  leave  the  rest  to  lie  fallow  until,  at  last, 
he  almost  loses  the  power  of  using  them  at  all.  The  fierce- 
ness of  the  battle  of  life  especially  tends  to  produce  a  one-sided 
mental  development.  The  business  man,  for  example,  be- 
comes only  too  frequently  so  absorbed  in  money-getting  that 
he  loses  the  intellectual  joys  of  art,  science,  and  literature,  and 
becomes  a  mere  money-making  machine.  The  scientific  man 
has  often  no  appreciation  of  art  or  literature,  and  the  literary 
man  is  utterly  incapable  of  sympathy  with  science.  A  good 
collegiate  education  in  early  life,  on  a  broad  basis  of  mathe- 
matics, literature,  and  natural  science,  is  the  best  security 
against  such  deformed  mental  growth. 

Besides  exercise,  the  greatest  need  for  the  healthy  develop- 
ment of  the  brain  is  sufficient  sleep.  The  infant  sleeps  15 
to  20  hours,  the  young  child  12  to  14,  and  the  boy  of 
high-school  age  should  get  9  to  10  hours  of  sleep.  Those 
who  are  using  the  brain  require  more  sleep  than  those  who 


262  THE  HUM4N  BODY. 

are  doing  muscular  work,  and  no  student  can  safely  sleep  less 
than  nine  hours. 

In  order  that  the  brain  may  keep  in  its  best  working  order, 
it  must  work  with  ease  and  pleasure.  Probably  no  condition 
is  so  important  in  keeping  the  nervous  system  in  a  healthy 
state  as  enjoyment  of  work  and  cheerfulness  in  daily  life. 
Plays  and  games  which  give  the  keenest  enjoyment,  especially 
if  involving  physical  activity,  are  of  the  utmost  importance 
for  the  well-being  of  this  master  tissue  of  the  body. 


9* 


CHAPTER   XXI. 
THE   SENSES. 

Common  Sensation  and  Special  Senses. — Changes  in  many 
parts  of  our  bodies  are  accompanied  or  followed  by  states  of 
consciousness  which  we  call  sensations.  All  such  parts  (sensitive 
parts")  are  in  connection,  direct  or  indirect,  with  the  brain  by 
sensory  nerve  fibres.  Since  all  feeling  is  lost  in  any  region 
of  the  body  when  this  connecting  path  is  severed,  it  is  clear 
that  all  sensations,  whatever  their  primary  exciting  cause,  are 
finally  dependent  on  conditions  of  the  brain.  Since  all  nerves 
lie  within  the  body  as  circumscribed  by  the  skin,  one  might 
be  inclined  to  suppose  that  the  cause  of  all  sensations  would 
appear  to  be  within  our  bodies  themselves ;  that  the  thing  felt 
would  be  recognized  as  a  modification  of  some  portion  of  the 
person  feeling.  This  is  the  case  with  regard  to  many  sensa- 
tions :  headache,  toothache,  or  earache  gives  us  no  idea  of 
any  external  object ;  it  merely  suggests  to  each  one  a  particular 
state  of  a  sensitive  portion  of  himself.  As  regards  many 
sensations  this  is  not  so  ;  they  suggest  external  causes,  and  we 
ascribe  the  sensations  to  the  external  objects  as  their  properties. 
Thus  they  lead  us  to  the  conception  of  an  external  universe  in 
which  we  live.  A  knife  laid  on  the  skin  produces  changes  in 
the  skin  which  lead  us  to  think  that  we  feel  a  cold  heavy  hard 
thing  which  is  not  the  skin.  We  have,  however,  no  sensory 
nerves  going  into  the  knife  and  informing  us  directly  of  its 


264  THE  HUMAN  BODY. 

condition ;  what  we  really  feel  are  the  modifications  of  the 
body  produced  by  the  knife,  although  we  irresistibly  think  of 
them  as  properties  of  the  knife.  If,  however,  the  knife  cuts 
through  the  skin,  we  cease  to  feel  the  knife  and  experience 
pain,  which  we  think  of  as  a  condition  of  ourselves.  We  do 
not  say  the  knife  is  painful,  but  that  the  finger  is,  and  yet  we 
have,  so  far  as  sensation  goes,  as  much  reason  to  call  the  knife 
painful  as  cold.  Applied  one  way  it  produced  local  changes 
in  the  skin  arousing  a  sensation  of  cold,  and  in  another  local 
changes  causing  a  sensation  of  pain.  Nevertheless  in  the  one 
case  we  speak  of  the  cold  as  being  in  the  knife,  and  in  the 
other  of  the  pain  as  being  in  the  finger. 

Those  sensitive  parts,  such  as  the  surface  of  the  skin,  through 
which  we  get  information  about  the  outer  world  are  of  far 
more  intellectual  value  to  us  than  such  parts,  as  the  subcutane- 
ous tissue,  which  give  us  sensations  referred  only  to  conditions 
of  our  own  bodies.  The  former  are  called  organs  of  special 
sense  ;  the  latter  possess  common  sensation. 

Common  Sensations  are  numerous,  as,  for  example,  pain, 
hunger,  nausea,  thirst,  satiety,  and  fatigue. 

Hunger  and  Thirst  regulate  the  taking  of  food.  Local 
conditions  play  a  part  in  their  production,  but  general  states 
of  the  body  are  also  concerned. 

Hunger  in  its  first  stages  is  due  to  a  condition  of  the  gastric 
mucous  membrane  which  comes  on  when  the  stomach  has 
been  empty  some  time.  It  may  be  temporarily  stilled  by 
filling  the  stomach  with  indigestible  substances,  but  soon  the 
feeling  comes  back  intensified  and  can  be  allayed  only  by  the 
ingestion  of  nutritive  materials.  Provided  that  these  are 
absorbed  and  reach  the  blood  their  mode  of  entry  is  not 
essential ;  hunger  may  be  stayed  by  injections  of  food  into 
the  intestine  as  completely  as  by  filling  the  stomach  with  it. 


THE  VISUAL  APPARATUS.  265 

Similarly,  thirst  may  be  temporarily  relieved  by  moistening 
the  throat  without  swallowing,  but  soon  returns ;  whereas  it 
may  be  permanently  relieved  by  water  injections  into  the  veins, 
without  wetting  the  throat  at  all. 

Both  sensations  depend  in  part  on  local  conditions  of 
sensory  nerves,  but  especially  on  the  poverty  of  the  blood  in 
foods  or  water,  which  leads  to  changes  in  nerve  cells.  It  has 
even  been  inferred  that  there  are  hunger  and  thirst  centres  of 
the  brain  which  are  thus  stimulated. 

The  Special  Senses  are  commonly  described  as  five  in 
number,  sight,  hearing,  touch,  smell,  and  taste,  but  to  these 
we  must  add  several  others. 

The  Visual  Apparatus  consists  of  nervous  tissues  immedi- 
ately concerned  in  giving  rise  to  sensations,  supported,  pro- 
tected, and  nourished  by  other  parts.  Its  essential  parts  are 
(i)  the  retina,  a  thin  membrane  lying  in  the  eyeball  and  con- 
taining microscopic  elements  which  are  so  acted  upon  by 
light  as  to  stimulate  (2)  the  optic  nerve;  this  nerve  ends  in  (3) 
the  visual  centre  of  the  brain,  which  when  stimulated  arouses 
in  our  consciousness  a  feeling  or  sensation  of  sight.  The 
visual  centre  may  be  excited  in  very  many  ways,  and  quite 
independently  of  the  optic  nerve  or  of  the  retina,  as  is 
frequently  seen  in  delirious  persons,  in  whom  inflammation  or 
congestion  of  the  brain  excites  directly  the  visual  centre  and 
gives  rise  to  visual  hallucinations. 

Usually,  however,  the  cerebral  visual  centre  is  excited  only 
through  the  optic  nerve,  and  the  optic  nerve  only  by 
light  acting  upon  the  retina.  The  eyeball,  containing  the 
retina,  is  so  constructed  that  light  can  enter  it,  and  so  placed 
and  protected  in  the  body  that  as  a  general  thing  no  other 
form  of  energy  can  act  upon  it  so  as  to  stimulate  the  retina. 
Under  exceptional  circumstances  we  may  have  sight  sensa- 


266  THE  HUMAN  BODY. 

tions  when  no  light  reaches  the  eye.  Anything  which  stimu- 
lates the  retina,  so  long  as  it  is  connected  by  the  optic  nerve 
with  the  cerebral  visual  centre,  will  cause  a  sight  sensation. 
A  severe  blow  on  the  eye,  even  in  complete  darkness,  will 
cause  the  sensation  of  a  flash  of  light ;  the  compression  of  the 
eyeball  excites  the  retina,  the  retina  excites  the  optic  nerve, 
the  optic  nerve  the  visual  nerve  centre,  and  the  result  is  a 
sight  sensation.* 

The  Eye  Socket. — The  eyeball  is  lodged  in  a  bony  cavity 
the  orbit,  open  in  front.      Each  orbit  is  a  pyramidal  chamber 
containing  connective  tissue,  blood  vessels,  nerves,  and  much 
fat.     The  fat  forms  a  soft  cushion  on  which  the  back  of  the 
eyeball  rolls. 

The  Eyelids  are  folds  of  skin,  strengthened  by  cartilage 

*  The  fact  that  sight  sensations  may  be  aroused  quite  independently  of 
all  light  acting  upon  the  eye  is  paralleled  by  similar  phenomena  in  re- 
gard to  other  senses,  and  is  of  fundamental  psychological  and  metaphys- 
ical importance.  That  a  blow  on  the  closed  eye  gives  rise  to  a  vivid 
light  sensation,  even  in  the  absence  of  all  actual  light,  proves  that  our 
sensation  of  light  is  quite  a  different  thing  from  light  itself.  The  visual 
sensory  apparatus,  it  is  true,  is  so  constructed  and  protected  that  of  all 
the  forces  of  nature,  light  is  the  one  which  far  more  frequently  stimulates 
it.  But  as  regards  the  peculiarity  in  the  quality  of  the  sensation  which 
leads  us  to  classify  it  as"  a  visual  sensation,"  that  peculiarity  has  nothing 
to  do  with  any  property  of  light.  The  visual  nerve  centre  when  stimu- 
lated causes  a  sight  sensation,  whether  it  has  been  excited  by  light,  by  a 
blow,  or  by  electricity.  Similarly  the  auditory  brain  centre  gives  us  a 
sound  sensation  when  stimulated  by  actual  external  sound  waves,  by 
a  blow  on  the  ear,  or  by  disease  of  the  auditory  organ.  One  kind  of 
energy,  light,  excites  more  often  than  any  other  the  visual  nerve  appa- 
ratus; another,  sound,  the  auditory  nerve  apparatus;  a  third,  pressure,  the 
touch  nerve  organs.  Hence  we  come  to  associate  light  with  visual  sen- 
sations and  to  think  of  it  as  something  like  our  sight  feelings;  to  imagine 
sound  as  something  like  our  auditory  sensations;  and  so  forth.  As  a 
matter  of  fact  both  light  and  sound  are  merely  movements  of  ether  or  air; 
it  is  our  own  stimulated  nerve  centres  which  produce  visual  and 
auditory  sensations;  the  ethereal  or  aerial  vibrations  merely  act  as 
the  stimuli  which  give  rise  to  nervous  impulses  in  the  nervous  apparatus. 


THE  LACHRYMAL  APPARATUS.  267 

and  moved  by  muscles.  Opening  along  the  edge  of  each 
eyelid  are  from  twenty  to  thirty  minute  glands,  called  the 
Meibomian  follicles.  Their  secretion  is  sometimes  abnormally 
abundant,  and  then  appears  as  a  yellowish  matter  along  the 
edges  of  the  eyelids,  which  often  dries  in  the  night  and 
causes  the  lids  to  be  glued  together  in  the  morning.  The 
eyelashes  are  curved  hairs,  arranged  in  one  or  two  rows  along 
each  lid.  They  help  to  keep  dust  from  falling  into  the  eye, 
and,  when  the  lids  are  nearly  closed,  protect  it  from  a  daz- 
zling light. 

The  Lachrymal  Apparatus  consists  of  a  tear  gland  in  each 
orbit,  of  ducts  which  carry  its  secre- 
tion   to    the    upper    eyelid,    and    of 
canals   by  which  this,   unless  exces- 
sive, is  carried  off  from  the  front  of 
the  eye  without  running  down  over    LD 
the    face.       The    lachrymal    or   tear 
gland,  about  the  size  of  an  almond,      FIG.  126.  Front  view  of  left 

eye,  with  eyelid  partly  removed 

lies  in  the  upper  and  outer  corner  of  to  show  lachrymal  gland,  L.G, 

and  lachrymal  duct,  L.D. 

the  orbit.  It  is  a  compound  race- 
mose gland,  from  which  twelve  or  fourteen  ducts  run  and  open 
on  the  inner  surface  of  the  upper  eyelid  at  its  outer  corner. 
The  secretion  spreads  evenly  over  the  exposed  part  of  the  eye 
by  the  movements  of  winking,  and  keeps  it  moist.  It  is  drained 
off  by  two  lachrymal  canals,  one  of  which  opens  by  a  small  pore 
on  an  elevation,  or  papilla,  near  the  inner  end  of  the  margin 
of  each  eyelid.  The  aperture  of  the  lower  canal  can  be  readily 
seen  by  examining  its  papilla  in  front  of  a  looking  glass.  The 
canals  run  inward  and  open  into  the  lachrymal  sac,  which  lies 
just  outside  the  nose,  in  a  hollow  where  the  lachrymal  and 
superior  maxillary  bones  (L  and  MX,  Fig.  16)  meet.  From 
this  sac  the  nasal  duct  proceeds  and  opens  into  the  nose 


268 


THE  HUM/IN  BODY. 


chamber  below  the  interior  turbinate  bone  (g,  Fig.  46, 
p.  no). 

Tears  are  constantly  being  secreted,  but  ordinarily  in  such 
quantity  as  to  be  drained  off  into  the  nose,  from  which  they 
flow  into  the  pharynx  and  are  swallowed.  When  the  lachry- 
mal duct  is  stopped  up,  however,  their  continual  presence 
makes  itself  unpleasantly  felt,  and  may  need  the  aid  of  a 
surgeon  to  clear  the  passage.  In  weeping  the  secretion  is 
increased,  and  then  not  only  more  of  it  enters  the  nose,  but 
some  flows  down  the  cheeks.  The  frequent  swallowing  move- 
ments of  a  crying  child  are  due  to  the  collection  of  tears  in 
the  pharynx. 

Movements  of  the  Eyeball. — Six  muscles  connect  the  eye- 
ball with  the  wall  of  the  cavity  containing  the  eye.  Four  of 


FIG.  127. — A ,  the  muscles  of  the  right  eyeball  viewed  from  above  ;  /?,  the  muscles 
of  the  left  eyeball  viewed  from  the  outer  side  ;  S.R,  superior  retcus  ;  Inf.R,  inferior 
rectus  ;  E.R,  external  rectus  ;  S.Ob,  superior  oblique;  Inf. Ob,  inferior  oblique; 
//,  the  optic  nerves  ;  ch,  their  crossing  or  chiasma  ;  ///,  the  third  cranial  nerve. 

these  are  attached  around  the  entrance  of  the  optic  nerve  at 
the  back  of  the  socket  and  extend  forward,  to  be  inserted  into 
the  eyeball  near  the  edge  of  the  transparent  front  part  (corned]. 
These  are  called  the  recti,  or  straight,  muscles  (Fig.  88,  3), 
and  are  further  named  according  to  their  position,  external, 


THE  EYEBALL  269 

internal,  superior,  and  inferior.  Each  muscle  when  contract- 
ing rotates  the  eye  toward  itself.  Two  muscles,  the  oblique, 
are  attached  to  the  sides  of  the  orbit  and  inserted  into  the 
eyeball  behind  the  recti. 

The  motions  of  the  eye  produced  by  these  muscles  are 
chiefly  from  right  to  left  and  up  and  down.  A  combination 
of  these  two  motions  permits  the  eye  to  be  turned  in  any  di- 
rection. The  eyes  are  so  controlled  through  the  nerves  stim- 
ulating the  muscles,  that  the  axial  lines  of  the  globes  of  the 
eyes  converge  to  pass  through  whatever  object  is  looked  at ; 
hence  the  axes  of  the  eyes  are  parallel  to  each  other  only  when 
one  looks  at  a  distant  object. 

The  Globe  of  the  Eye  is  on  the  whole  spheroidal,  but  con- 
sists of  segments  of  two  spheres  (Fig.  128).  A  portion  of  a 
sphere  of  small  radius  forms  its  anterior  transparent  part,  and 
is  set  upon  the  front  of  its  posterior  segment,  which  is  part  of 
a  larger  sphere.  In  general  terms  it  may  be  described  as  con- 
sisting of  three  coats  and  three  refracting  media. 

The  outer  coat  (i  and  3,  Fig.  128)  consists  of  the  sclerotic 
and  the  cornea.  The  cornea  is  transparent  and  is  situated  in 
front ;  the  sclerotic  is  opaque  and  white  and  covers  the  back, 
sides  and  a  part  of  the  front  of  the  globe,  where  it  is  seen 
between  the  eyelids  as  the  white  of  the  eye.  Both  are  com- 
posed of  dense  connective  tissue  and  are  tough  and  strong. 

The  second  coat  consists  of  the  choroid  (9,  10)  and  the 
iris  (14).  The  choroid  consists  mainly  of  blood  vessels  sup- 
ported by  loose  connective  tissue,  which  in  its  inner  layers 
contains  many  dark  brown  or  black  pigment  granules.* 
Towards  the  front  of  the  eyeball,  where  it  begins  to  diminish 
in  diameter,  the  choroid  separates  from  the  sclerotic  and  turns 

*  In  pink-eyed  rabbits  and  occasionally  in  human  beings  this  pigment 
is  absent. 


270  THE  HUMAN  BODY. 

i  n  to  form  the  iris,  the  colored  part  of  the  eye  which  is  seen 
through  the  cornea.  In  the  centre  of  the  iris  is  a  circular 
dark  aperture,  the  pupil,  through  which  light  reaches  the 
interior  of  the  eyeball. 


FIG.  128. — The  left  eyeball  in  horizontal  section  from  before  back,  i,  sclerotic;  2, 
junction  of  sclerotic  and  comea;  3,  cornea;  4,  5,  conjunctiva;  6,  posterior  elastic  layer 
of  cornea;  7,  ciliary  muscle  ;  10,  choroid  ;  n,  13,  ciliary  processes ;  14,  iris;  15,  retina; 
16,  optic  nerve  ;  17,  artery  entering  retina  in  optic  nerve  ;  18,  fovea  centralis  ;  19,  region 
where  sensory  part  of  retina  ends  ;  22,  suspensory  ligament ;  23  is  placed  in  the  canal  of 
Petit,  and  the  line  from  25  points  to  it ;  24,  the  anterior  part  of  the  hyaloid  membrane  ; 
26,  27,  28,  are  placed  on  the  lens  ;  28  points  to  the  line  of  attachment  around  it  of  the 
suspensory  ligament;  29,  vitreous  humor;  30,  anterior  chamber  of  aqueous  humor;  31, 
posterior  chamber  of  aqueous  humor. 

The  third  or  innermost  coat,  the  retina  (15),  is  the  essential 
part  of  the  eye,  since  in  it  the  light  produces  those  changes 
that  give  rise  to  nervous  impulses  in  the  optic  nerve.  It  lines 
the  posterior  half  of  the  eyeball. 

The  Microscopic  Structure  of  the  Retina  is  very  com- 
plex ;  although  but  -g1^  inch  in  thickness  it  presents  ten  dis- 
tinct layers. 


THE  RETINA. 


271 


Beginning  (Fig.  129)  with  its  front  or  inner  side  we  find 
the  internal  limiting  membrane  (i),  a  thin  structureless  layer; 


FIG.  129. — A  section  through  the  retina  from  its  anterior  or  inner  surface  (i)  in  contact 
with  the  hyaloid  membrane,  to  its  outer  (10)  in  contact  with  the  choroid  T,  internal 
limiting  membrane  ;  2,  nerve-fibre  layer;  3,  nerve  cell  layer;  4,  inner  molecular  layer ; 
5,  inner  granular  layer ;  6,  outer  molecular  layer ;  7,  outer  granular  layer ;  8,  external 
limiting  membrane  ;  9,  rod  and  cone  layer ;  10,  pigment  cell  layer. 


the  nerve  fibre  layer  (2),  formed  by  radiating  fibres  of  the 
optic  nerve  ;  the  nerve  cell  layer  (3);  the  inner  molecular  layer 
(4),  consisting  partly  of  very  fine  nerve  fibrils,  and  largely  of 


272  THE  HUMAN  BODY. 

connective  tissue;  the  inner  granular  layer  (5),  composed  of 
nucleated  cells  :  the  outer  molecular  layer  (6),  thinner  than  the 
inner;  the  outer  granular  layer  (7),  composed  of  thick  and 
thin  fibres  on  each  of  which  is  a  conspicuous  nucleus  with  a 
nucleolus  ;  the  thin  external  limiting  membrane  (8),  perforated 
by  apertures  through  which  the  rods  and  cones  (9)  of  the 
ninth  layer  join  the  fibres  of  the  seventh ;  and  outside  of  all, 
next  the  choroid,  the  pigmentary  layer  (10).  The  nerve  fibres 
are  believed  to  be  continuous  with  the  rods  and  cones. 
Light  entering  the  eye  passes  through  the  transparent  retina 
until  it  reaches  and  excites  the  rods  and  cones  which  stimu- 
late the  nerves. 

The  Blind  Spot. — Where  the  optic  nerve  enters  the  retina 
it  forms  a  small  elevation  (Fig.  130),  from  which  nerve  fibres 


I 

FIG.  130.— The  right  retina  as  it  would  be  seen  if  the  front  part  of  the  eyeball  with  the 
lens  and  vitreous  humor  were  removed.  The  white  disk  to  the  right  marks  the  entry  of 
the  optic  nerve  (blind  spot) ;  the  lines  radiating  from  this  are  the  retinal  arteries  and 
veins.  The  small  central  dark  patch  is  the  yellow  spot,  the  region  of  most  acute  vision. 

radiate.     This  elevation  possesses  neither  rods  nor  cones  and 
is  blind,  as  may  be  readily  demonstrated.     Close  the  left  eye 


THE  IRIS.  273 

and  look  steadily  with  the  right  at  the  cross   (Fig.    131), 
holding  the  page  vertically  in  front  of  the  face,  and  moving 


FIG.  131. 

it  alternately  from  and  toward  you.  When  the  book  is  about 
ten  inches  from  the  eye  the  white  disk  entirely  diappears  from 
view  because  its  image  then  falls  on  the  part  of  the  retina 
where  the  optic  nerve  enters. 

Light  consists  of  vibrations  in  an  ether  which  pervades 
space.  An  object  which  sets  up  no  waves  in  the  ether  does  not 
excite  the  visual  nervous  apparatus,  and  appears  black ;  an 
object  which  sets  up  ethereal  vibrations  capable  of  exciting  the 
rods  and  cones  of  the  retina  appears  white  or  colored.  The 
ethereal  vibrations  enter  the  eye  through  the  cornea,  pass 
on  through  the  pupil  and  lens  to  stimulate  the  retina. 

The  Iris. — In  the  front  portion  of  the  eye  behind  the 
transparent  cornea,  and  floating  in  the  aqueous  humor,  lies 
a  colored  curtain  (the  iris)  which  forms  a  circle,  with  a  hole 
(the  pupil)  in  its  centre.  The  iris  has  muscular  fibres  which 
enable  it  to  make  the  pupil  larger  or  smaller  according  as  the 
light  is  faint  or  bright.  All  the  light  which  goes  to  the  retina 
must  pass  through  the  pupil,  and  the  brightness  of  the  images 
on  the  retina  is  dependent  upon  the  number  of  rays  which 
find  their  way  through  ;  hence  a  large  opening  gives  brighter 
images  than  a  small  one.  The  iris  by  its  adjustment  of  the 


2 74  THE  HUM Atf  BODY. 

size  of  the  pupil  thus  reflexly  controls  the  amount  of  light 
and  keeps  the  retina  from  injury  by  excess.  It  has  another 
function :  when  we  look  at  near  objects  the  pupil  becomes 
smaller  than  when  we  look  at  distant  objects.*  The  iris  thus 
acts  as  the  diaphragm  of  a  camera,  since  it  is  possible  to  form 
a  sharp  image  of  a  near  object  only  with  a  small  bundle  of 
rays. 

When  there  is  little  light,  as  at  twilight,  the  pupils  are  large 
and  the  eye  cannot  make  distinct  images,  even  of  distant  ob- 
jects ;  hence  everything  seems  blurred. 

The  Refracting  Surfaces  of  the  Eye  are  three  in  number : 
(i)  the  anterior  surface  of  the  cornea,  (2)  the  anterior  sur- 
face of  the  crystalline  lens,  and  (3)  the  posterior  surface  of 
the  crystalline  lens  (Fig  128).  These  surfaces  act  together 
like  a  convex  lens,  to  bend  the  rays  of  light  which  pass 
through  them  (Fig.  132),  so  that  all  those  which  start  from 


FIG.  132.— Illustrating  the  formation  behind  a  convex  lens  of  a  diminished  and  in- 
verted image  of  an  object  placed  in  front  of  it. 

one  point  of  an  external  object  meet  again  in  a  focus  on  one 
point  of  the  retina.  In  this  way  small  and  inverted  images  of 
the  objects  at  which  we  look  are  formed  on  the  retina,  and 
stimulate  its  rods  and  cones. 

*  This  change  of  pupil  can  be  readily  seen  in  another's  eye  by  pressing 
the  hand  over  it  for  a  moment  or  two  and  then  removing  the  hand. 


ACCOMMODATION.  2  75 

Accommodation. — In  the  healthy  eyeball  the  crystalline 
lens  is  controlled  by  muscles  which  change  its  convexity, 
making  it  greater  when  we  look  at  near,  and  less  when  we 
look  at  distant,  objects.  Standing  at  a  window  behind  a  lace 
curtain  we  can  look  at  the  curtain  and  see  its  threads  plainly, 
but  while  so  doing  we  see  houses  on  the  other  side  of  the 
street  indistinctly,  because  the  convexity  of  the  lens  is  such 


FIG.  133. — Section  of  front  part  of  eyeball  showing  the  change  in  the  form  of  the  lens 
when  near  and  distant  objects  are  looked  at.  a,  c,  t>,  cornea  ;  ^ ,  lens  when  near  object 
is  looked  at ;  />',  lens  wh  n  distant  object  is  looked  at. 

as  to  focus  light  on  the  retina  from  the  near  object,  and  not 
from  the  distant.  We  can,  however,  "focus"  on  the  houses 
over  the  way  and  see  them  plainly ;  but  then  we  no  longer 
see  the  curtain  distinctly,  because  the  lens  has  changed  its 
form  to  focus  light  from  the  far  object  on  the  retina.  The 
eye  relaxes  to  focus  on  distant  objects,  and  a  muscular  effort 
is  necessary  to  increase  the  convexity  of  the  lens,  i.e.  accom- 
modate, for  near  objects. 

Short  Sight  and  Long  Sight. — In  the  normal  eye  the  range 
of  accommodation  is  very  great,  making  it  possible  to  focus 
on  objects  infinitely  distant  or  only  six  or  eight  inches 
from  the  eye.  In  the  natural  healthy  eye  parallel  rays  of 
light  meet  on  the  retina  when  the  muscles  controlling 
the  crystalline  lens  are  relaxed  and  the  lens  is  at  its  flattest 


2  76 


THE  HUMAN  BODY. 


(A,  Fig.  134).      Such  eyes  are  emmetropic  or  normal      In  some 
eyes  the  eyeball  is  elongated  and  when   not  accommodated 

parallel  rays  meet  in  front 
of  the  ret  i  na  (B)  .  Persons 
with  such  eyes  cannot  see 
distant  objects  distinctly 
without  the  aid  of  diverg- 
ing (concave)  spectacles  ; 
they  are  myopic  or  short- 
sighted. In  others,  the  eye- 
ball is  flattened,  and  when 
not  accommodated  parallel 
rays  are  brought  to*  a 
focus  behind  the  retina 
(C).  To  see  even  distant 
objects,  such  persons  must 
therefore  use  muscular 

effort  to  increase  the  COn- 

verging  power  of  the  lens; 
and  when  objects  are  near  they  cannot  bring  the  rays  pro- 
ceeding from  them  to  a  focus  soon  enough.  To  get  distinct 
retinal  images  of  near  objects,  they  therefore  need  converging 
(convex)  spectacles.  Such  eyes  are  called  hypermetropic  or 
far-sighted. 

Astigmatism.  —  The  refracting  surfaces  of  the  eye  acting 
together  are  equivalent  in  refracting  power  to  a  single,  spher- 
ical surface  of  fairly  short  curvature.  Frequently,  however, 
the  result  is  not  the  same  as  would  be  given  by  a  perfect 
spherical  surface,  owing  to  inequalities  in  the  curvature  of  the 
eye.  In  one  direction  the  curvature  may  be  greater  than 
that  at  right  angles  to  it.  This  tendency  to  a  cylindrical 
form  is  called  astigmatism.  It  interferes  with  the  formation 


Sic((oUmyopic  (S)'and  a  hypcrme- 


HYGIENE   OF  THE  EYES.  277 

of  perfect  images  and  sometimes  leads  to  serious  eye  strain  in 
the  effort  to  better  the  vision.  Astigmatism  may  be  de- 
tected by  looking  at  black  lines  radiating  from  a  point  or  at 


FIG.  135. — Lines  for  the  detection  of  astigmatism. 

fine  black  concentric  circles.  Portions  of  the  lines  or  circles 
appear  gray  and  others  black  ;  the  gray  portions  are  out  of 
focus.  This  defect  is  corrected  by  proper  cylindrical  glasses 
which  equalize  the  curvatures  of  the  eye. 

Hygiene  of  the  Eyes. — Since  the  healthy  eye  is  so  con- 
structed that  when  it  is  not  accommodated  it  forms  images  of 
distant  objects  on  the  retina,  muscular  effort  is  required  to  see 
near  objects,  and  fatigue  results  if  the  effort  is  long  con- 
tinued. 

In  a  hypermetropic  eye  still  more  effort  is  needed  to  see 
near  objects,  and  this  results  in  greater  muscular  fatigue. 
Hypermetropic  persons  can  often  read  well  for  a  while,  but 
then  complain  that  they  can  no  longer  see  distinctly.  This 
kind  of  weak  sight  should  always  lead  to  examination  of  the 
eyes  by  an  oculist;  otherwise  severe  headaches  may  result  and 
the  eyes  be  injured. 

Children  sometimes  have  hypermetropic  eyes,  and  should 
be  at  once  provided  with  suitable  glasses.  In  old  age  another 
kind  of  far-sightedness  (presbyopia}  is  common,  due  to  stiff- 


278 


THE  HUMAN  BODY. 


ness  of  the  crystalline  lens,  which  cannot  become  convex 
enough  during  accommodation  to  focus  the  images  of  near 
objects  on  the  retina. 

Short-sighted  eyes  appear  to  be  more  common  now  than 
formerly,  especially  in  those  who  use  the  eyes  constantly  at 
short  range.  Myopia  is  rare  among  those  who  live  mainly 
out  of  doors.  It  is  not  so  apt  to  lead  to  permanent  injury 


FIG.  136.  —Semi-diagrammatic  section  through  the  right  ear.  M,  concha  ;  G,  external 
auditory  meatus ;  'J\  tympanic  or  drum  membrane  ;  P,  middle  ear ;  o,  oval  foramen  ; 
r,  round  foramen.  Extending  from  T  to  o  is  seen  the  chain  of  tympanic  bones.  /?, 
Eustachian  tube.  V,  B,  S,  bony  labyrinth  :  I',  vestibule  ;  B,  semicircular  canal ;  S, 
cochlea,  b,  I,  /',  membranous  semicircular  canal  and  vestibule.  A,  auditory  nerve  di- 
viding into  branches  for  vestibule,  semicircular  canal,  and  cochlea. 

of  the  eye  as  hypermetropia,  but  the  effort  to  see  dis- 
tinctly any  but  near  objects  is  apt  to  produce  headaches 
and  other  symptoms  of  nervous  exhaustion.  Eye  strain 
frequently  shows  itself  in  headaches  and  general  nervous 
symptoms  which  do  not  appear  to  be  associated  with  the 
eyes.  They  are,  however,  relieved  when  the  eyes  are  cor- 


HEARING— THE  EAR. 


279 


rected  by  glasses.  The  general  health  also  reacts  upon 
the  eyes  and  tends  to  exaggerate  the  nervous  effects  of  eye 
strain. 

Hearing. — The  ear  (Fig.  136)  consists  of  three  portions, 
known  respectively  as  the  external  ear,  the  middle  ear,  and  the 
internal  ear  or  labyrinth.  The  latter  is  the  essential  hearing 
organ  since  it  contains  the  ends  of  the  auditory  nerve  fibres. 

The  External  Ear  consists  of  the  expansion  (M),  seen  on 
the  exterior  of  the  head,  called  the  concha,  and  a  passage 
leading  in  from  it,  the  external  auditory  meatus  (G).  This  pass- 
age is  closed  at  its  inner  end  by  the  tympanic  membrane  or  drum 
(T).  It  is  lined  by  a  prolongation  of  the  skin,  through  which 
numerous  small  glands,  secreting  the  wax  of  the  ear,  open. 

The  Middle  Ear,  or  drum  chamber  of  the  ear  (Fig.  137 
and  P,  Fig.  136),  is 
an  irregular  cavity  in 
the  temporal  bone, 
closed  externally  by 
the  drum  membrane. 
From  its  inner  side  £,- 
the  Eustachian  tube 
(R,  Fig.  136)  pro- 
ceeds and  opens  into 
the  pharynx.  This 
tube  allows  air  from 
the  throat  to  enter  the 
cavity,  and  serves  to 

keep  equal  the    atmOS-      FIG    137— The  middle  ear  and  its  bones,  considerably 
.  magnified      G,   the  inner  end  of  the   external  auditory 

pneriC        pressure        On  meatus,  closed  internally  by  the  conical  tympanic  mem- 
brane ;  /,,  the  malleus,  or  hammer-bone;  //,  the  incus, 
ach.  side    Of  the    drum  or  anvil-bone  ;  S,  the  stapes,  or  stirrup-bone. 

membrane.*     Three   small  bones   (Fig.   137)   stretch  across 
*  Frequently  the  inflammation  of  sore  throat  extends    into  the  Eusta- 


280  THE  HUMAN  BODY. 

the  cavity  from  the  drum  membrane  to  the  labyrinth ;  they 
transmit  the  vibrations  of  the  membrane,  produced  by  sound 
waves  in  the  external  air,  to  the  liquid  of  the  labyrinth.  The 
outmost  bone  is  the  hammer  or  malleus  ;  the  inmost,  the  stirrup 
or  stapes  ;  and  the  middle  bone,  the  anvil  or  incus. 

The  Internal  Ear,  or  Labyrinth,  consists  primarily  of 
chambers  and  tubes  hollowed  out  in  the  temporal  bone. 
The  middle  chamber,  called  the  vestibule  (  F,  Fig.  135),  has 
an  opening,  the  oval  foramen  (0),  in  its  outer  side,  into  which 
the  inner  end  of  the  stapes  fits.  Behind,  the  vestibule  opens 
into  three  semicircular  canals  (one  of  which  is  shown  at  B, 
Fig.  135),  and  in  front  into  a  spirally  coiled  tube  («$"),  the 
cochlea.  In  these  bony  chambers  and  tubes  lie  membranous 
chambers  and  tubes,  in  which  the  fibres  of  the  auditory  nerve 
(A,  Fig.  135)  end.  All  the  labyrinth  chamber  outside  these 
membranous  parts  is  occupied  by  a  watery  liquid,  known  as 
perilymph.  The  membranous  chambers  are  filled  with  a  sim- 
ilar liquid,  the  endolymph. 

The  cochlea  consists  essentially  of  a  tube  coiled  upon  itself 
something  like  a  snail  shell.  Partitions  running  through  the 
length  of  the  tube  divide  it  into  three  cavities  (Fig.  138), 
the  middle  and  triangular-shaped  cavity,  which  contains  the 
auditory  nerve  terminals,  and  two  side  cavities.  Each  cavity 
is  filled  with  endolymph.  The  membrane  which  divides  the 
tube  into  nearly  equal  parts  is  called  the  basilar  membrane. 
This  supports  the  structure  known  as  the  organ  of  Corti  in 
which  the  nerve  terminals  end  (Fig.  138).  The  rods  and 
cells  which  form  the  organ  of  Corti  are  continued  with  the 
basilar  membrane  throughout  the  length  of  the  cochlea.  The 

chian  tube  and  closes  it.  The  air  in  the  cavity  of  the  middle  ear  is  then 
absorbed  and  permits  the  external  air  to  press  the  drum  in,  producing 
more  or  less  deafness. 


THE  COCHLEA.  281 

organ  of  Corti  and  the  basilar  membrane  form  a  series  of 
vibrating  cords  with  corresponding  nerve  apparatus  for  re- 
ceiving vibrations  transmitted  from  the  bones  of  the  ear 


FIG.  138. — Diagram  of  a  section  of  a  coil  of  the  cochlea.  C  C,  canal  of  the  cochlea  ; 
mR,  its  upper  wall ;  Sc.  V,  the  part  of  the  bony  cavity  above  the  canal  of  the  cochlea  ; 
Sc.'JT,  the  part  below  it;  O.C,  the  organ  of  Corti  on  the  basilar  membrane;  A.JV, 
branch  of  auditory  nerve  in  the  central  column  of  the  spiral  ;  a,  connective  tissue  cush- 
ion to  which  the  basilar  membrane  is  attached;  b,  the  bony  walls;  m.t,  a  membrane 
lying  over  the  organ  of  Corti ;  l.s,  the  spiral  ledge  projecting  from  the  axis. 

through  the  endolymph  of  the  ear  and  for  transforming  them 
into  nervous  impulses.  The  vibrating  cords  of  the  basilar 
membrane  are  so  arranged  that  they  can  respond  to  vibrations 


282  THE  HUMAN  BODY. 

varying  in  rapidity  from  30  to  about  20,000  per  second. 
Each  portion  of  the  membrane  has  its  own  rate  of  vibration 
and  is  set  in  motion  by  vibrations  of  the  same  rate  trans- 
mitted to  it  from  the  external  air.  Any  vibrations  in  the  en- 
dolymph  will  pick  out  the  portions  of  the  basilar  membrane 
with  corresponding  vibrations  and  thus  selectively  create  ner- 
vous impulses  in  the  corresponding  nerve  terminals  in  the 
organ  of  Corti.  These  impulses  transmitted  to  the  auditory 
centre  give  rise  to  sensations  which  we  recognize  as  sounds. 

Sound. — The  sensation  which  we  know  as  sound  is  origi- 
nated by  oscillations  produced  in  the  air  by  vibrating  bodies, 
such  as  a  piano  string  or  an  organ  pipe.  A  musical  lone  is 
caused  by  a  regular  succession  of  such  oscillations.  Loud- 
ness  depends  upon  the  extent,  pitch  upon  the  rapidity  of 
vibration  ;  slow  vibrations  give  rise  to  deep,  rapid  vibra- 
tions to  shrill,  tones.  A  1 6-inch  organ  pipe  and  the  lowest 
string  of  the  piano  give  about  33  vibrations  to  the  second, 
their  octave  66,  and  so  on,  doubling  for  each  octave.  A 
pure  tone  is  of  one  pitch  throughout,  but  each  vibrating  body 
gives  out  a  complex  sound  made  up  of  the  vibration  as  a 
whole  {fundamental  /one),  together  with  vibrations  of  parts 
of  itself  (overtones').  The  quality  which  enables  us  to  dis- 
tinguish between  a  piano  and  a  violin,  an  organ  or  the  human 
voice,  depends  upon  the  richness  and  character  of  these  over- 
tones. It  is  called  color,  or  timbre. 

The  Semicircular  Canals  are  associated  with  the  sense  of 
equilibrium. 

Nerves  are  distributed  to  the  ends  of  the  semicircular 
canals  and  terminate  in  cells  with  hairs  (Fig.  139).  These 
hairs  project  into  the  endolymph  of  the  cavity.  They 
are  arranged  so  that  when  an  individual  is  standing  one 
canal  of  each  ear  is  horizontal,  the  second  is  vertical 


SKIN  OR   DERMAL  SENSES. 


283 


antero-posteriorly,  and  the  third  is  in  the  vertical  plane 
at  right  angles  to  the  second. 
Motion  in  any  direction 
gives  rise  to  a  movement  of 
endolymph  through  the  hairs 
of  the  cells,  just  as  water  in  a 
bucket  which  is  suddenly 
rotated  moves  along  the 
inner  surface  of  the  bucket. 
This  causes  pressure  upon  the 
hairs  and  leads  to  the  trans- 
mission of  nervous  impulses 
which  in  turn  give  rise  to 

JIG.   139.— Diagram  of  epithelium  in  ner- 
the    Sensation     Of    movement  vous  reSion  of  ampulla  of  a  semicircular  canal. 

and  equilibrium.  Persistent  dizziness  has  frequently  led  to 
diagnoses  of  disease  in  this  region. 

Skin  or  Dermal  Senses. — Many  sensory  nerves  end  in  the 
skin  through  which  we  get  several  kinds  of  sensation.  When 
a  pencil  point  is  pressed  against  the  skin,  we  have  a  sense  of 
touch  and  of  pressure ;  when  pressed  very  strongly,  a  sense  of 
pain.  When  the  point  is  pressed  very  lightly  upon  various 
points  an  occasional  cold  point  is  discovered.  When  a  warm 
point  is  applied  the  sense  of  warmth  is  distinct  and  strong  at 
certain  points  in  the  skin  and  weak  at  others.  Each  special 
sensation  is  probably  due  to  a  special  nerve  ending  and  nerve, 
capable  of  translating  the  stimuli  (whether  change  of  tem- 
perature, pressure,  etc.)  into  nervous  impulses  which  give  rise 
in  the  brain  to  the  corresponding  sensation.* 

By  combinations  of  these  sensations  we  get  the   charac- 

*  This  is  a  marked  illustration  of  the  fact  that  nerves  transmit  special 
kinds  of  nervous  impulses  or  have  specific  energy  (specific  energy  of 
nerves}. 


284  THE  HUMAN  BODY. 

teristics  of  the  objects  that  we  touch,  of  hardness,  softness, 
smoothness,  roughness,  heat  or  cold,  size,  if  the  object  is 
small  enough  to  be  received  as  a  unit,  and  number,  if  several 
objects  are  applied  to  the  skin  at  once,  provided  they  are  not 
too  near  together. 

The  Localization  of  Skin  Sensations. — When  the  eyes  are 
closed  and  a  point  of  the  skin  is  touched  we  can  with  some 
accuracy  indicate  the  region  stimulated ;  because,  although 
tactile  feelings  are  alike  in  general  characters,  they  differ  in 
something  (local  sign]  besides  intensity  by  which  we  can  dis- 
tinguish them  as  originated  on  certain  parts  of  the  skin. 
The  fineness  of  the  localizing  power  varies  widely  in  different 
skin  regions,  and  is  measured  by  observing  the  least  distance 
which  must  separate  two  objects  (as  the  blunted  points  of  a 
pair  of  compasses)  in  order  that  they  may  be  felt  as  two. 
The  following  table  illustrates  some  of  the  differences  ob- 
served : 

Tongue-tip 1. 1  mm.     (.04  inch) 

Palm  side  of  last  phalanx  of  finger 2.2  mm.     (.08  inch) 

Red  part  of  lips 4.4  mm.     (.  16  inch) 

Tip  of  nose 6.6mm.     (.24  inch) 

Back  of  second  phalanx  of  finger n.o  mm.    (.44  inch) 

Heel 22.0  mm.     (.88  inch) 

Back  of  hand 30.8  mm.  (1.23  inches) 

Forearm 39.6  mm.  (1.58  inches) 

Sternum 44-O  mm.  (1.76  inches) 

Back  of  neck 52.8  mm.  (2.  n  inches) 

Middle  of  back 66.0  mm.  (2.64  inches) 

It  is  supposed  that  the  variations  in  discriminating  power 
are  dependent  upon  the  richness  of  distribution  of  the  tactile 
nerve  ends,  and  that  one  or  more  untouched  terminals  must 
lie  between  those  on  which  the  compass  points  rest  in  order 
that  two  points  may  be  distinguished. 


THE  MUSCULAR.  SENSE. 


285 


The  Muscular  Sense. — Movements  of  the  limbs  are  accom- 
panied by  a  sensation  of  effort,  which  is  proportional  to  the 


FIG.  140. — Section  of  skin  showing  two  papillae  of  the  dermis  and  some  of  the  deeper 
cells  of  the  epidermis.  «,  papilla  containing  blood  vessels;  6,  papilla  containing  a 
tactile  corpuscle,  t ;  </,  medullated  nerve  fibres  going  to  the  corpuscle  ;  at/,  optical  cross- 
sections  of  the  fibres  are  seen  as  they  wind  round  the  outside  of  the  corpuscle  ;  the 
general  transverse  direction  of  the  connective  tissue  bundles  of  the  capsule  of  the 
corpuscle  is  shown. 

energy  expended  and  enables  one  to  estimate  the  weight  of 
the  object  moved  and  the  direction  of  movement.  These 
sensations  have  been  called  the  muscular  sense.  They  have 
been  attributed  to  many  causes  and  are  now  supposed  to  be 
due  to  a  complex  of  nervous  impulses  received  from  joints, 
muscles,  tendons,  skin,  etc.  They  give,  in  addition  to  sense 
of  effort  and  of  direction  of  movement,  a  sense  of  the  position 
of  the  limbs.  The  muscular  sense  is  exceedingly  important  as 
a  subconscious  guide  to  muscular  control. 

Pain  may  be  described  as  a  general  sensation,  since  it  has 
no  special  locality  or  peculiarity  of  manifestation.  In  general 
it  is  a  danger  signal  to  prevent  injury,  and  guide  to  the  way  of 
health.  While  abnormal  conditions  in  all  tissues  and  organs 
may  give  rise  to  pain,  the  skin  is  far  more  sensitive  than  the 
deeper  structures.  Experiments  suggest  that  there  may  be 


286 


THE  HUMAN  BODY. 


special  pain  nerves,  although  their  special  terminal  structure 

has  not  been  identified. 

Smell. — The  endings  of  the  olfactory  nerves  are  spread  in 

the  mucous  membrane  of  the  upper  parts  of  the  nasal  cavities. 

The  olfactory  cells  are  distributed 
between  the  cells  of  the  mucous 
membrane  (Fig.  141)  and  send 
fine  filaments  out  to  the  surface. 
They  are  scattered  over  the  upper 
and  lower  turbinate  bones  (o,  p, 
Fig.  46)  (which  are  expansions 
of  the  ethmoid  on  the  outer  wall 
of  the  nostril  chamber),  the 
opposite  part  of  the  partition 
between  the  nares  and  that  part 
of  the  roof  of  the  nose  (n,  Fig. 
46)  which  separates  it  from  the 
cranial  cavity. 

Odorous  Substances,  the  stim- 
uli of  the  olfactory  apparatus,  are 
FIG. .141—  Ceils  from  the  olfactory  ordinarily    gaseous.      They    fre- 

epithehum.     i,  from  the  frog.     2,  from 

man ;  a,  columnar  cell,  with  its  branched            ntjy  act       powerfully       when 

deep  process  ;  6,  so-called  olfactory  cell;  Huv- 

c,    its    narrow    outer    process;     ,/,    its  nresent  jn    very    sma]l     Quantity 

slender  central  process.     3,  gray  nerve  prCSCIlL  1  1    VCiy     . 

fibres  of  the  olfactory  nerve,  seen  di-     .  c            •,     •,         .    • 

viding  into  fine  peripheral  branches  at  a.  A  gram  Or  tWO  of  mUSk  kept  in  a 

room  will  give  the  air  in  it  an  odor  for  years,  and  yet  at  the  end 
will  hardly  have  diminished  in  weight.  While  some  gases  or 
vapors  have  this  powerful  influence  upon  the  olfactory  organ, 
others,  as  pure  air,  do  not  stimulate  it  at  all.* 

Tas^e. — The  organ  of  taste  is  the  mucous  membrane  on 

*  In  ordinary  breathing,  the  air  passes  through  the  lower  part  of  the 
nose  and  therefore  does  not  reach  the  o'.factory  surface.  In  "sniffing," 
the  air  is  passed  directly  over  this  surface. 


TASTE.  287 

the  upper  side  of  the  tongue,  and  possibly  on  the  soft  palate 
and  fauces.  The  mucous  membrane  of  the  tongue  presents 
innumerable  elevations  or  papillae  (Fig.  53)  of  three  kinds 
(p.  116).  The  filiform  papillae  are  organs  of  touch,  for  the 
tongue  has  the  sense  of  touch  as  well  as  of  taste.  The  cir- 
cumvallate  and  fungi  form  papillae  contain  the  endings  of 
branches  of  the  glosso-pharyngeal  and  trigeminal  nerves  (pp. 
241,  242),  which,  when  excited  by  bodies  in  solution, 
stimulate  the  taste  centres  in  the  brain. 

Many  so-called  tastes  (flavors)  are  really  smells ;  odorif- 
erous particles  of  substances  which  are  being  eaten  reach  the 
nose  through  the  posterior  nares  and  arouse  smell  sensations 
which,  since  they  accompany  the  presence  of  objects  in  the 
mouth,  we  take  for  tastes.  Such  is  the  case  with  most  spices, 
since  when  the  nasal  chambers  are  closed  by  a  cold  in  the 
head  or  by  pinching  the  nose,  the  so-called  "taste  "  of  spices 
is  not  perceived,  but  only  a  certain  pungency  due  to  stimula- 
tion of  nerves  of  common  sensation  in  the  tongue. 


CHAPTER   XXII. 
VOICE  AND  SPEECH. 

Voice  consists  of  sounds  produced  by  the  vibrations  of  two 
elastic  folds  called  the  vocal  cords.  These  cords  lie  in  the 
larynx,  which  is  situated  between  the  pharynx  and  the  wind- 
pipe, and  is  a  portion  of  the  air  passage  specially  modified  to 
form  a  voice  organ. 

The  vocal  cords  project  into  the  larynx  so  that  only  a  nar- 
row slit,  the  glottis,  is  left  between  them.  When  they  are  put 
in  a  certain  position  the  air  driven  through  the  glottis  sets 
them  vibrating  and  they  give  rise  to  sounds.  The  stronger 
the  blast  the  louder  the  voice. 

The/#c^  of  the  voice  is  primarily  dependent  on  the  size  of 
the  larynx.  The  longer  the  vocal  cords  are,  the  lower  is  the 
pitch  of  the  voice.  Children,  in  whom  the  larynx  is  small, 
have  shrill  voices  ;  and  for  the  same  reason  a  woman's  voice 
is  usually  higher  pitched  than  a  man's.  About  sixteen  or 
seventeen  years  of  age  a  boy's  larynx  grows  very  fast,  and 
his  voice  becomes  about  an  octave  deeper  in  tone. 

While  every  one's  voice  has  a  certain  natural  pitch  which 
leads  us  to  call  it  soprano,  tenor,  bass,  and  so  forth,  this  pitch 
can  be  modified  within  limits,  so  that  we  each  can  sing  a 
number  of  notes.  This  variety  is  due  to  the  action  of  muscles 
in  the  larynx  which  alter  the  tension  of  the  vocal  cords. 

288 


RESONANCE— SPEECH.  289 

The  more  tightly  they  are  stretched  the  higher  pitched  is  the 
tone  which  they  emit. 

Resonance. — Although  musical  instruments  depend  prima- 
rily upon  vibrating  bodies,  yet  the  volume  and  quality  of  their 
tones  are  largely  determined  by  resonance  chambers,  as  in  the 
cornet  and  organ,  or  by  sounding  boards,  as  in  the  piano  and 
violin.  When  a  tuning  fork  is  held  in  the  ringers  and  tapped 
it  gives  a  very  low  tone.  When,  however,  it  is  touched  to  a 
hollow  box  open  at  one  end  and  so  constructed  that  the  air 
column  contained  in  it  will  vibrate  in  unison  with  the  tuning 
fork,  the  volume  and  purity  of  the  sound  are  enormously  in- 
creased. 

The  pharynx,  mouth  and  nose  cavities  act  as  a  resonance 
chamber  for  the  vibrations  of  the  vocal  cords,  picking  out  and 
reinforcing  the  tones  to  which  the  air  contained  in  them  cor- 
responds in  rate  of  vibration.  When  the  vocal  cords  vibrate 
they  set  the  air  in  vibration.  The  sound  is  made  louder  and 
changed  in  character  by  this  selective  emphasis  on  fundamen- 
tal tones  and  overtones. 

Speech. — By  movements  of  throat,  soft  palate,  tongue, 
cheeks,  and  lips,  the  size  and  form  of  the  resonance  chamber 
are  varied,  and  with  them  the  tone  of  voice.  By  movements 
of  tongue,  lips,  and  palate,  the  air  current,  and  therefore  the 
sound,  is  interrupted  from  time  to  time,  or  the  air  is  forced 
through  a  narrow  passage  in  the  mouth,  giving  rise  to  sounds 
in  addition  to  those  originated  by  the  vocal  cords.  The 
primitive  feeble  monotonous  tone  due  to  the  vibration  of  the 
vocal  cords  is  thus  reinforced  and  altered  in  throat  and 
mouth,  and  voice  is  developed  into  articulate  speech. 

The  Larnyx  consists  of  a  framework  of  nine  cartilages,  mov- 
ably  articulated  together,  and  having  muscles  attached  to  them 
by  whose  contractions  their  relative  positions  are  altered. 


290  THE  HUMAN  BODY. 

These  cartilages  form  a  tube,  continuous  with  the  windpipe 
and  lined  by  mucous  membrane.     At   one   level  the   vocal 


FIG.  142.— The  more  important  cartilages  of  the  larynx  from  behind,  t,  thyroid  ;  Cs, 
its  superior,  and  Ci,  its  interior,  horn  of  the  right  side  ;  **,  cricoid  cartilage  ;  t,  aryte- 
noid  cartilage  ;  Pv,  the  corner  to  which  the  posterior  end  of  a  vocal  cord  is  attached  ; 
Pm,  corner  on  which  the  muscles  which  approximate  or  separate  thejvocal  cords  are  in- 
serted ;  co,  cartilage  of  Santorini. 

cords,  also  covered  with  mucous  membrane,  project  into  the 
tube,  leaving  for  the  passage  of  air  only  the  narrow  slit  of  the 
glottis. 

The  largest  cartilage  of  the  larnyx  (/,  Fig.  142)  is  the 
thyroid.  It  is  placed  in  front  and  consists  of  right  and  left 
halves  which  meet  at  an  angle  in  front,  but  separate  behind 
so  as  to  enclose  a  V-shaped  space.  The  front  of  the  thyroid 
cartilage  causes  the  prominence  in  the  neck  known  as  Adam's 
apple.  The  epiglottis,  not  represented  in  the  figure,  is  at- 
tached to  the  top  of  the  thyroid  cartilage  and  overhangs  the 
entry  from  pharynx  to  larynx.  It  may  be  seen,  covered 
by  mucous  membrane,  projecting  at  the  root  of  the  tongue,  if 


THE   VOCAL   CORDS-LARYNGEAL   MUSCLES.        291 

the  mouth  is  held  open  before  a  mirror,  and  the  tongue  held 
down.  It  is  represented  as  seen  from  behind  at  a,  Fig.  143. 
The  cricoid  cartilage  (**,  Fig.  142)  has  the  form  of  a  signet- 
ring,  with  its  broad  part  turned  toward  the  back  of  the  throat, 
and  placed  in  the  lower  part  of  the  opening  between  the 
halves  of  the  thyroid.  The  two  arytenoid  cartilages  (•)-,  Fig. 
142)  are  placed  on  the  top  of  the  wide  posterior  part  of  the 
cricoid;  each  is  pyramidal  in  form.  The  remaining  laryn- 
geal  cartilages  are  of  less  importance. 

The  Vocal  Cords,  which  are  rather  projecting  pads  of  elas- 
tic tissue  than  cords  in  the  ordinary  sense  of  the  word,  pro- 
ceed, one  from  each  arytenoid  cartilage  behind,  to  the  angle 
where  the  halves  of  the  thyroid  meet  in  front.  When  open, 
as  in  quiet  breathing,  the  glottis  (c,  Fig.  143)  is  narrow  in 
front  and  wider  behind,  and  since  air  driven  through  the 
opening  does  not  then  set  the  margins  of  the  cords  in  vibra- 
tion, no  sound  is  produced. 

The  Muscles  of  the  Larynx. — The  laryngeal  muscles  are 
numerous.  One  set  of  muscles  pulls  the  arytenoid  cartilages 
towards  one  another  and  thus  narrows  the  glottis  behind  ;  air 
forced  through  the  narrowed  slit  causes  vibration  of  the  cords 
and  produces  voice.  Another  set  stretches  and  tightens  the 
vocal  cords  by  pulling  the  arytenoid  cartilages  backward,  and 
thereby  raises  the  pitch  of  the  voice.  A  third  set  pulls  the 
front  of  the  thyroid  cartilage  nearer  the  arytenoids  and  so 
slackens  the  cords  and  lowers  the  pitch  of  the  voice.  A 
fourth  set  separates  the  arytenoid  cartilages,  and  with  them 
the  vocal  cords,  and  thus  widens  the  glottis  and  allows  air  to 
pass  through  it  without  producing  voice. 

The  Range  of  the  Human  Voice  from  the  lowest  note  (f 
of  the  unaccented  octave)  of  an  ordinary  bass  to  the  highest 
note  (£•  on  the  thrice  accented  octave)  of  a  fairly  good  so- 


292 


THE  HUMAN  BODY. 


prano  is  about  three  octaves  :   the  former  note  is  produced  by 
88   vibrations  per  second     the  latter  by   792.     Celebrated 


11 


11 


FIG.  143. — The  larynx  viewed  from  its  pharyngeal  opening.  The  back  wall  of  the 
pharynx  has  been  divided  and  its  edges  (n)  turned  aside,  i,  body  of  hyoid  ;  2,  its 
small,  and  3,  its  great,  horns  ;  4,  upper  and  lower  horns  of  thyroid  cartilage;  5,  mucous 
membrane  of  front  of  pharynx,  covering  the  back  of  the  cricoid  cartilage  ;  6,  upper 
end  of  gullet ;  7,  windpipe,  lying  in  front  of  the  gullet ;  8,  eminence  caused  by  carti- 
lage of  Santorini ;  9,  eminence  caused  by  cartilage  of  Wrisberg — both  lie  in,  10,  the 
aryteno-epiglottidean  fold  of  mucous  membrane,  surrounding  the  opening  (aditus 
laryngis)  from  pharynx  to  larynx;  «,  projecting  tip  of  epiglottis;  c,  the  glottis— the 
lines  leading  from  the  letter  point  to  the  free  vibrating  edges  of  the  vocal  cords ;  <£', 
the  ventricles  of  the  larynxt — heir  upper  edges,  marking  them  off  from  the  eminences 
£,  are  the  false  vocal  cords. 

singers  of  course  go  beyond  this  limit  in  each  direction  : 
basses  have  been  known  to  take  a  on  the  great  octave  (55 
vibrations  per  second),  and  Mozart,  at  Parma,  heard  a  soprano 


VOWELS  AND  CONSONANTS.  293 

sing  a  note  of  the  extraordinarily  high  pitch  c  on  the  fifth 
accented  octave  (2114  vibrations  per  second). 

Vowels  are  musical  tones  produced  in  the  larynx  and  mod- 
ified by  resonance  of  the  air  in  the  pharynx  and  mouth.  To 
get  the  broad  a  sounds,  as  ah,  the  mouth  is  widely  opened 
and  the  lips  drawn  back.  Such  vowels  as  oo  (moor)  are  pro- 
duced by  protruding  the  lips  and  lengthening  the  mouth  cav- 
ity. The  change  in  the  form  of  the  mouth  may  be  noticed  by 
pronouncing  consecutively  the  vowel  sounds  a^,  eh,  ee,  oh,  oo. 
The  English  i  (as  in  spire)  is  a  diphthong,  consisting  of  a 
(p#d)  followed  by  e  (feet),  as  may  be  readily  found  on  at- 
tempting to  sing  a  sustained  note  to  the  sound  i. 

Semivowels. — In  uttering  true  vowel  sounds  the  soft  palate 
is  raised  so  as  to  shut  off  the  resonance  of  the  nasal  cavity. 
For  some  other  sounds  (the  semivowels  or  resonants)  the  initial 
step  is,  as  in  the  case  of  the  true  vowels,  the  production  of  a 
laryngeal  tone ;  but  the  soft  palate  is  not  raised,  and  the 
mouth  exit  is  more  or  less  closed  by  the  lips  or  the-  tongue  ; 
hence  the  blast  issues  partly  through  the  nose,  which  by  its 
resonance  gives  them  a  special  character,  as  in  the  case  of  m, 
n,  and  ng. 

Consonants  are  sounds  produced  not  mainly  by  the  vocal 
cords,  but  by  modifications  of  the  expiratory  blast  on  its  way 
through  the  mouth.  The  current  may  be  interrupted  and  the 
sound  changed  by  the  lips  (labials,  as/  and  3);  or,  at  or  near 
the  teeth,  by  the  tip  of  the  tongue  (dentals,  as  /and  d);  or, 
in  the  throat,  by  the  root  of  the  tongue  and  the  soft  palate 
{gutturals,  as  k  and  g). 

Consonants  may  also  be  classified  by  the  kind  of  move- 
ment which  gives  rise  to  them.  In  explosives  an  interruption 
to  the  air  current  is  suddenly  interposed  or  removed  (/,  b,  t, 
d>  %)  £")•  Other  consonants  are  continuous  (ft  s,  r)  and  may 


294  THE  HUMAN  BODY. 

be  divided  into  (i)  aspirates,  when  the  air  is  made  to  rush 
through  a  narrow  aperture,  as,  for  example,  between  the  lips 
(/"),  the  teeth  (j),  the  tongue  and  the  palate  (^),  or  the 
tongue  and  the  teeth  (M);  (2)  resonants  or  semivowels;  (3) 
vibratories,  the  different  forms  of  r,  due  to  vibrations  of  parts 
bounding  a  constriction  put  in  the  way  of  the  air  current  on 
its  passage. 


CHAPTER   XXIII. 
GROWTH   AND   NUTRITION. 

Development. — The  human  body,  like  the  bodies  of  all 
animals,  begins  life  as  a  single  cell.  This  single  cell  divides 
to  form  two,  these  in  turn  form  four,  and  so  the  process  of 
division  {segmentation)  continues  until  there  is  a  mulberry- 
like  mass  of  cells  which  do  not  appear  to  differ  one  from 
another  and  which  occupy  about  the  same  space  as  the 
original  cell  (Fig.  144).  From  this  time  on  the  continued 


FIG.  144. — A,  an  ovum;   B  to  £,  successive  stages  in   its  segmentation  until  the 
morulat  J?,  is  produced  ;  n,  cell  sac  ;  £,  cell  contents  ;  <r,  nucleus. 

increase  in  number  is  accompanied  by  an  increase  in  bulk. 
The  cells  no  longer  follow  the  same  course  of  growth,  but 
groups  of  cells  develop  peculiarities  of  their  own,  according 

295 


296  THE  HUMAN  BODY. 

to  a  process  known  as  differentiation.  Ultimately  three  lay- 
ers are  formed.  Each  of  these  layers  continues  differen- 
tiating, with  the  result  that  from  one  layer  the  skin  and  the 
central  nervous  system  are  developed ;  from  another  the  mus- 
cular and  bony  system ;  and  from  the  third  the  alimentary 
tract. 

The    tissues   resulting    from    this   differentiation   may   be 
roughly  classified  in  the  following  manner : 

(1)  Undifferentiated    tissues.       These    are   composed    of 
cells  with  no  special  development,    retaining  much   of  the 
form  and  properties  of  rudimentary  cells.      Lymph  corpuscles 
and  some  of  the  white  blood  corpuscles  belong  to  this  class. 

(2)  Supporting    tissues,    including    cartilage,    bone,    and 
connective  tissue. 

(3)  Nutritive  tissues,  including  those  cells  which  have  to 
do  with  the  reception  and  preparation  of  food,  the  secretion 
of  digestive  fluids,  and  the  excretion  of  waste  matters  ;  as,  for 
example,  the  cells  of  the  stomach,  intestines,  lungs,  kidneys, 
and  skin,  and  the  glands  of  the  alimentary  tract. 

(4)  Storage    tissues,    represented    by  the  liver  cells  and 
such  connective  tissue  cells  as  become  loaded  with  fat. 

(5)  Irritable  tissues,  as  the  sense  organs. 

(6)  Co-ordinating   and   automatic  tissues,   as   the    nerve 
cells. 

(7)  Motor   tissues,    represented   by   ciliated  and   muscle 
cells. 

(8)  Conductive  tissues,  as  nerve  fibres. 

(9)  Protective  tissues,   including  the  epithelial  lining  of 
the  cavities  of  the  body,  the  epidermis,  hairs,  nails,  and  the 
enamel  of  the  teeth. 

(10)  Reproductive  tissues,   by  which   the  ovum  with   its 
power  of  developing  into  a  new  individual  is  produced. 


CELL  NUTRITION.  297 

The  cells  making  up  the  various  tissues  of  the  body  have 
characteristic  forms  and  powers.  Cells  with  like  powers, 
together  with  supporting  cells,  are  grouped  into  masses 
called  organs.  These  organs  are  placed  in  such  positions  as 
will  interfere  least  with  the  activity  of  the  body  as  a  whole, 
and  will  best  subserve,  by  their  special  activities,  its  welfare. 
The  functions  of  any  organ  are  the  sum  of  the  functions  of 
the  cells  composing  it.  These  cells  may  all  have  the  same 
work  to  do,  as  in  muscle,  or  may  have  different  work,  as  in 
the  glands  of  the  stomach,  some  cells  of  which  secrete  pepsin, 
others  hydrochloric  acid,  while  both  secrete  water. 

Cell  Nutrition. — Each  cell  has  work  to  do  for  the  body 
as  a  whole ;  it  has  also  to  look  after  its  own  well-being  in 
order  to  be  able  to  do  its  work.  This  means  that  each  cell 
of  the  bodies  of  the  higher  animals  must  take  food  materials 
in  the  form  of  serum  albumin  or  globulin,  sugar,  oxygen,  etc., 
must  combine  them  into  a  compound  which  is  capable  of 
ready  oxidation  for  the  liberation  of  energy,  must  then  be 
prepared  to  liberate  this  energy  under  the  stimulation  of  nerve 
impulses,  must  direct  the  energy  into  useful  channels,  and 
get  rid  of  the  waste  products  of  oxidation.  It  must  appro- 
priate substance  and  build  it  up  into  its  own  protoplasm  for 
growth  or  repair.  That  these  changes  in  cells  may  be  con- 
siderable is  shown  by  Fig.  145. 

All  the  activities  of  the  cell  are  stimulated  and  controlled 
by  impulses  received  through  connected  nerves.  The  nervous 
impulses  which  have  to  do  with  the  nutrition,  growth,  and 
general  condition  of  the  cell  itself  are  supposed  to  be  distinct 
from  the  impulses  which  stimulate  the  cell  to  work  for  the 
body  as  a  whole,  and  have  even  been  supposed  to  be  trans- 
mitted to  the  cell  through  special  nerves  (trophic  nerves^. 
The  cell  may  thus  be  considered  an  individual  member 


298  THE  HUMAN  BODY. 

of  a   community  with   certain  duties   and  privileges  of  its 
own. 


d 


FIG.  145  —Serous  glands,  a,  rabbit's  pancreas  "  loaded  "  (resting) ;  c ,  "  discharged  " 
(active)  (observed  in  the  living  animal)  (Kuhne  and  Lea).  £,  loaded  ;  </,  discharged, 
alveolus  of  parotid  (fresh  preparations)  (Langley). 

General  Nutrition. — We  have  seen  that  the  cells  making 
up  the  body  have  work  to  do  both  for  themselves  and  for  the 
other  cells  of  the  body,  thus  forming  a  vast  army  with  one 
general  plan  of  campaign.  While  we  have  definite  knowl- 
edge of  many  of  the  general  conditions  under  which  the 
cells  work,  and  of  their  contributions  to  the  human  economy, 
yet  there  is  much  which  we  do  not  know.  When  the  body 
is  deprived  for  a  considerable  time  of  certain  salts  and  acids, 
it  becomes  weak  and  diseased  (scurvy),  but  we  do  not  know 
in  what  the  efficacy  of  the  acids  and  salts  consists.  We  can 
only  infer  that  they  influence  the  cells  and  enable  them  to  do 
their  work  better.  Again,  up  to  a  certain  point  an  increase 
of  exercise  for  the  cells  of  the  body  means  an  increase  of 
power,  and  apparently  their  full  power  is  not  reached  unless 
this  opportunity  for  practice  and  exercise  is  given  them. 
When  thus  exercised  they  become  larger  as  well  as  more 
effective.  Other  tissues  than  those  exercised  also  feel  the 
stimulus.  This  is  especially  true  of  the  exercise  of  the  mus- 


ANIMAL  HEAT— HEAT  CONTROL  299 

cles,  which  seems  able,  by  making  indirect  demands  upon  the 
other  cells  of  the  body,  to  bring  about  the  full  development 
of  all.  Even  the  passive  tissues,  such  as  bone  and  tendon, 
are  influenced  through  muscular  exercise. 

Animal  Heat. — Cellular  activity  produces  energy  in  forms 
useful  to  the  body,  including  heat.  We  have  seen  that  a 
certain  amount  of  heat  is  necessary,  since  all  the  tissues  of  the 
body  work  best  at  a  temperature  of  39°  C.  (98°  .5  F.).  It 
is  easily  demonstrated  that  under  normal  conditions  the  tem- 
perature of  the  body  remains  constant  at  this  optimal  temper- 
ature throughout  life. 

Muscular  activity  furnishes  far  more  heat  than  any  other 
form  of  activity  in  the  body.  It  has  been  found  by  experi- 
ment that  of  the  potential  energy  set  free  in  the  oxidation  of 
material  in  the  muscles  two  thirds  appear  as  heat,  whereas  only 
one  third  does  work  as  muscular  energy.  Heat  is,  therefore, 
developed  in  proportion  to  the  amount  of  muscular  work 
done,  and  in  hard  work  a  much  larger  amount  of  heat  is  pro- 
duced than  is  necessary  to  maintain  the  body  temperature. 
This  excess  of  heat  becomes  a  waste  product  which  must  be 
got  rid  of  in  order  to  prevent  a  rise  in  body  temperature 
(fever). 

Heat  Control. — A  definite  mechanism  for  the  control  of 
the  heat  loss  exists  in  the  body  to  insure  the  maintenance  of 
the  best  temperature.  The  heat  is  carried  by  the  blood  from 
the  heat-producing  centres,  muscles,  glands,  etc.,  to  all  parts 
of  the  body,  including  exposed  inactive  tissues,  such  as  the 
skin,  lungs,  ears,  nose,  fingers  and  toes.  The  presence  of  an 
excess  of  heat  reflexly  stimulates  the  blood  vessels  of  the  skin 
to  dilate  and  the  perspiratory  glands  to  secrete.  The  result 
is  that  a  large  mass  of  blood  is  thrown  into  contact  with  the 
cooler  surface  of  the  body,  which  is  being  still  further  cooled 


300  THE  HUMAN  BODY. 

by  the  evaporation  of  the  moisture.  The  blood  rapidly  loses 
its  heat  and  goes  back  to  the  interior  parts  of  the  body 
cooler,  again  to  take  up  the  heat,  carry  it  to  the  surface  and 
get  rid  of  it.  An  increased  amount  of  heat  is  also  got  rid  of 
by  the  lungs  during  the  more  rapid  breathing  accompanying 
severe  work. 

During  rest  a  reverse  process  takes  place.  The  blood  ves- 
sels ,qf  the  skin  reflexly  contract,  keeping  the  blood  within 
the  interior  of  the  body,  which  is  now  protected  from  heat 
loss  by  a  thick  layer  of  skin  and  fat.  This  process  of  vaso- 
motor  control  has  been  likened  to  the  taking  off  and  putting 
on  of  an  overcoat.  Cold  blooded  animals  are  without  this 
mechanism  and  have  a  variable  temperature,  dependent  upon 
that  of  the  medium  in  which  they  are.  In  summer  a  frog 
may  have  a  temperature  of  100°  F.,  in  winter  of  33°  or 
34°  F. 

Fever.— In  the  condition  known  as  fever,  the  temperature 
of  the  body  is  raised  above  the  normal.  This  is  thought  to 
be  due  in  most  cases  to  the  following  factors :  first,  reduction 
in  the  amount  of  perspiration  which  ordinarily  accompanies 
fever  (dry  skin),  hence  diminished  heat  loss  through  its 
evaporation ;  second,  increased  production  of  heat  by  un- 
usual activity  and  consequent  heat  formation  in  the  tissues ; 
and  third,  disarrangement  of  the  heat-controlling  nerve 
mechanism. 

Fever  is  not  primarily  a  disease,  but  a  symptom  of  several 
diseases,  and  depends  upon  varying  conditions  rather  than 
upon  any  one  factor. 

Internal  Secretion  of  Glands. — We  have  seen  that  some 
glands  secrete  fluids  which  they  carry  through  ducts  to  sur- 
faces more  or  less  remote  from  themselves.  There  are  certain 
glands  of  the  body,  as  the  spleen,  the  thyroid  gland,  etc., 


INTERNAL  SECRETION  OF  GLANDS.  3O1 

which  have  no  ducts  and  whose  only  connection  with  the  rest 
of  the  body  is  by  means  of  the  blood  passing  in  through  the 
artery  and  out  through  the  vein ;  hence  their  secretion  must 
be  given  to  the  blood  to  be  carried  to  the  rest  of  the  body 
(internal  secretion) .  This  makes  it  very  difficult  to  determine 
the  real  functions  of  these  organs  experimentally,  since  large 
amounts  of  blood  pass  through  them  in  twenty-four  hours,  and 
substances,  even  if  given  off  in  considerable  quantities  in  their 
secretions,  are  so  greatly  diluted  as  to  escape  detection. 

The  spleen  is  situated  in  the  left  side  of  the  abdominal  cav- 
ity under  the  eleventh  rib.  It  is  a  large  mass  of  cellular  tissue 
supported  by  a  framework  of  connective  tissue,  into  which 
the  blood  escapes  from  the  open  ends  of  the  blood  vessels  in 
its  passage  through  it.  In  malaria  and  in  certain  blood 
diseases  associated  with  a  large  increase  of  white  blood  cor- 
puscles the  spleen  becomes  greatly  enlarged.  Apart  from  its 
function  of  giving  off  white  blood  corpuscles,  little  is  known 
of  the  spleen,  as  it  can  be  removed  without  serious  results. 

The  thyroid  gland,  which  lies  on  either  side  and  below  the 
larynx ;  the  thymus  gland,  which  is  found  near  the  thyroid  \ 
the  suprarenal  capsule,  the  small  gland  lying  above  each 
kidney ;  and  the  pituitary  body,  a  very  small  gland  lying  at 
the  base  of  the  brain,  are  other  examples  of  ductless  glands. 

That  these  last  named  glands  have  important  functions  is 
shown  by  cases  of  disease  and  by  experiments  made  on  ani- 
mals in  which  the  glands  were  removed.  When  the  thyroid 
gland  is  removed  from  the  body,  the  tissues  become  more  or 
less  gelatinous,  the  animal  weakens  and  soon  dies.  When 
the  secreting  cells  of  the  thyroid  gland  are  destroyed  in  man 
by  disease,  a  similar  condition  of  the  tissues  follows.  If  the 
thyroid  glands  from  pig  or  sheep  are  then  eaten,  the  tissues 
again  recover  their  character  and  strength  is  regained,  show- 


3° 2  THE  HUMAN  BODY. 

ing  a  definite  relation  between  the  abnormal  condition  of  the 
tissues  and  the  secretion  of  the  glands. 

Removal  of  the  suprarenal  capsules  leads  quickly  to  death. 
Disease  of  the  capsules  is  associated  with  muscular  weakness 
and  pigmentation  or  bronzing  of  the  skin.  Experiments  have 
shown  that  the  secretion  of  these  capsules  is  undoubtedly 
closely  associated  with  the  vaso-motor  control  of  blood  vessels. 

Removal  of  the  pituitary  body  leads  also  to  rapid  death, 
with  symptoms  somewhat  resembling  the  removal  of  the 
thyroid  gland.  Disease  of  the  pituitary  body  in  man  is  asso- 
ciated with  a  curious  condition  of  enlargement  of  the  bones 
of  the  body  {giantism}. 

Experiments  have  shown  that  the  kidney,  beside  its  func- 
tion of  the  external  secretion  (excretion)  of  urine  from  the 
blood,  acts  apparently  as  a  ductless  gland.  When  three 
quarters  of  the  secreting  substances  of  the  two  kidneys  have 
been  removed  (one  half  of  one  kidney  and  the  whole  of  the 
other),  the  secretion  of  urine  is  carried  on  adequately,  but  the 
animal,  in  spite  of  a  voracious  appetite,  rapidly  wastes  away 
and  dies,  showing  that  the  kidney  must  contribute  to  the 
blood  substances  essential  to  health. 

Removal  of  the  pancreas  or  disease  affecting  certain  of  its 
cells  leads  to  a  secretion  of  sugar  from  the  kidney  (diabetes) 
and  to  a  rapid  wasting  of  the  body  and  final  death. 

Experiments  have  shown  that  an  animal  cannot  survive  the 
removal  of  the  liver,  although  the  entire  secretion  of  the  bile 
may  be  poured  out  on  the  surface  of  the  body  through  a  fistula 
and  lost  without  serious  harm.  This  shows  that  its  internal 
secretion  is  also  of  extreme  importance. 

The  essential  result  of  interference  with  the  internal  secre- 
tions of  the  glands  seems  to  be  a  profound  disturbance  of 
nutrition,  which,  though  it  assumes  various  aspects,  is  distinctly 


HEALTH— DISEASE.  3°3 

related  to  the  power  of  the  cells  in  assimilating  and  utilizing 
food  material  and  in  performing  their  work. 

Health. — We  have  seen  that  the  cells  of  the  body  act  as 
individuals  in  the  work  of  the. body,  and  that  their  efforts  are 
controlled  by  the  nervous  system,  in  order  that  a  balanced 
effort  toward  the  one  end  of  maintaining  the  body's  effective 
power  may  be  obtained.  We  may  therefore  define  health  as 
that  condition  in  which  the  work  of  each  cell  of  the  body  is 
perfectly  done  through  the  proper  co-ordination  and  balance 
of  all. 

Disease  thus  becomes  a  condition  in  which  the  working 
power  of  cells  in  a  part  of  the  body  is  reduced  or  lost  or  the 
balance  destroyed.*  Tissue  cells  are  hindered  in  their  work 
or  even  destroyed  by  certain  minute  unicellular  parasitic 
plants  called  bacteria.  Some  of  these  have  the  power  of  de- 
veloping in  the  body,  interfering  with  its  balance,  and 
directly  destroying  the  cells  of  the  tissues.  They  also  develop 
poisonous  substances  through  their  own  activity  (pto- 
maines),! which,  when  carried  away  by  the  blood,  may 
overwhelm  the  vital  powers  and  finally  produce  death. 

Immunity  from  Disease. — Certain  diseases  are  commu- 
nicated from  individual  to  individual  and  are  classed  as 
contagious  and  probably  bacterial,  though  this  has  not  been 
demonstrated  in  the  case  of  all.  The  most  common  are  scar- 
let fever,  diphtheria,  smallpox,  typhoid  fever,  yellow  fever, 
cholera,  plague,  and  tuberculosis  (consumption).  In  some 
of  these  diseases,  as  measles,  mumps,  and  scarlet  fever,  one 

*  Some  diseases  are  not  thoroughly  understood  and  cannot  be  classified 
in  this  way.  Most  diseases,  however,  come  within  the  two  classes 
named. 

f  These  disease-producing  bacteria  may  be  .  grown  on  certain  sub- 
stinces  as  bouillon,  gelatin,  potato,  etc.  When  thus  cultivated  they  give 
rise  to  substances  among  the  most  poisonous  known. 


3°4  THE  HUM/IN  BODY. 

attack  ordinarily  protects  against  a  second  attack  and  the 
individual  thus  protected  is  said  to  be  immune  to  them. 

It  has  been  recently  shown  by  experiments  that  when  the 
blood  of  an  animal  which  has  recently  had  the  disease  is  inject- 
ed into  the  blood  of  another  animal,  it  will  give  the  latter  im- 
munity, even  against  the  disease  germs  when  inoculated  directly 
into  its  tissues.  This  has  been  applied  in  certain  diseases, 
notably  diphtheria,  in  the  following  manner  : — The  poisonous 
substance  (Joxiri}  developed  in  cultures  of  diphtheria  bacilli, 
and  carefully  filtered  to  remove  all  living  bacilli,  is  injected 
into  a  horse  in  successive  doses,  each  one  so  small  that  it  is 
not  fatal.  After  weeks  or  months  of  continuous  dosing,  the 
horse  is  apparently  perfectly  well  and  vigorous.  The  serum 
of  its  blood  when  injected  into  the  subcutaneous  lymph  spaces 
and  thence  absorbed  into  the  blood  of  a  man  is  capable  of 
making  all  the  tissues  of  the  body  unfriendly  to  the  diphtheria 
bacilli,  and  of  protecting  the  individual  entirely  from  their 
ravages.  More  than  this,  it  may  even  be  capable,  under 
favorable  circumstances,  of  destroying  bacilli  which  have 
already  a  foothold  and  have  produced  the  symptoms  of  diph- 
theria. It  is  inferred  that  a  new  substance  {antitoxin)  has  thus 
been  formed  in  the  horse's  blood.  The  production  of  the 
antitoxin  is  apparently  a  distinct  reaction  of  the  body  to  the 
stimulus  of  the  toxin  in  such  a  way  as  to  neutralize  its  bad 
effect,  provided  that  the  vitality  of  the  tissues  has  not  been 
already  too  far  lowered  by  an  overwhelming  amount  of  toxin. 

The  immunity  gained  by  a  previous  attack  of  the  disease  is 
in  like  manner  probably  due  to  the  antitoxin  developed  in  the 
body  as  a  reaction  to  the  toxin  of  the  disease.  Since  vacci- 
nation protects  against  smallpox,  it  is  probable  that  cowpox 
(vaccinia)  is  a  modified  form  of  smallpox. 

The  immunity  of  scarlet  fever,  smallpox  and  yellow  fever 


IMMUNITY  FROM  DISEASE.  3° 5 

may  last  for  years  or  even  for  life,  whereas  that  of  diphtheria 
is  for  a  few  weeks  only ;  of  tuberculosis  none  has  been  dis- 
covered. Whether  this  difference  is  due  to  the  fact  that  the 
antitoxin  is  produced  by  the  body  only  during  the  presence  of 
the  toxin  (i.e.  during  the  disease)  and  that  the  duration  of  the 
immunity  depends  upon  the  rapidity  with  which  the  antitoxin 
is  eliminated  from  the  body,  or  that  the  formation  of  the  anti- 
toxin by  the  tissues  continues,  after  being  once  started  by 
the  toxin,  for  periods  which  vary  in  different  diseases,  has 
not  been  determined.  It  is  probable  that  the  power  of  the 
tissues  to  develop  the  protective  substances  is  limited  and  is 
perfect  only  in  a  few  diseases.  It  may  be  possible,  however, 
eventually,  by  the  use  of  animals  for  the  development  of  anti- 
toxins or  for  the  modification  of  disease-producing  bacilli,  to 
stamp  out  contagious  diseases  by  giving  immunity,  as  has 
been  done  in  the  case  of  smallpox. 


APPENDIX  A. 

EMERGENCIES. 

SUFFOCATION. 

Suffocation — Gas  Poisoning. — In  cases  where  a  person  is 
deprived  of  oxygen,  the  vital  powers  may  become  so  much 
depressed  that  life  appears  extinct.  This  may  be  due  to  in- 
terference with  the  act  of  breathing ;  to  the  presence  of  gas, 
as  carbon  dioxide  or  illuminating  gas,  in  such  quantities  as 
to  displace  the  oxygen ;  to  submersion  in  water ;  or  to  en- 
closure in  a  small  space  from  which  the  oxygen  is  readily 
used  up  in  the  regular  process  of  breathing  and  cannot  be 
renewed.  Ordinarily  suffocation  is  complicated  with  poison- 
ing by  gases.  * 

Treatment : — Remove  the  patient  into  the  fresh  air.  Dash 
cold  water  into  the  face,  slap  the  chest  and  tickle  the  nose. 
Hold  ammonia  under  the  nostrils  or  take  the  tongue  in  a  dry 
handkerchief  and  every  four  seconds  draw  it  out  with  moder- 
ate force.  If  these  measures  fail  to  re-establish  breathing, 
artificial  respiration  must  be  immediately  undertaken. 

Artificial  Respiration  is  used  in  all  cases  of  suffocation 
and  drowning  in  which  natural  respiratory  movements  have 

*  Illuminating  gas  contains  the  very  poisonous  gas,  carbon  monoxide, 
which  unites  with  the  haemoglobin  of  the  blood  to  displace  the  oxygen  in 
the  red  corpuscles. 

307 


EMERGENCIES. 

ceased.  If  an  individual  has  been  under  water,  the  lungs 
are  naturally  filled  with  water  and  should  be  at  once  emptied. 
Turn  him  on  his  face,  clasp  your  hands  under  the  lower 
chest  and  raise  him  from  the  ground;  the  pressure  upon 
the  lower  chest  will  compress  the  lungs  and  tend  to  empty 
them  of  water.  Repeat  two  or  three  times,  taking  care  not 
to  injure  the  face  by  rough  handling.  Do  not,  however, 
delay  artificial  respiration  in  the  attempt  to  remove  all  of  the 
water. 

Wipe  out  the  mouth  and  throat.  Turn  the  patient  over  on 
his  back  with  something  under  his  back  and  shoulders  so  that 
the  head  will  rest  well  back.  Pass  a  pin  through  the  tip  of 
the  tongue.  Draw  the  tongue  out  from  the  mouth ;  pass  a 
string  around  it  back  of  the  pin,  cross  it  over  the  chin  and 
tie  it  behind  the  head  so  that  the  tongue  will  be  held  for- 
ward and  will  not  close  the  air  passage  into  the  larynx.* 
Loosen  the  clothing,  and,  if  wet,  cover  it  with  dry. 

Place  yourself  at  the  head  of  the  patient,  grasp  his  fore- 
arms near  the  elbow  and  carry  them  upward  so  that  they  lie 
parallel  at  each  side  of  his  head  (Fig.  146).  Let  them  rest 
there  for  a  moment ;  notice  that  air  enters  through  the  nose 
and  mouth.  Then  carry  the  arms  back  and  press  them  upon 
the  chest  (Fig.  147)  ;  notice  that  air  is  expired.  Repeat 
this  regularly  every  three  or  four  seconds. 

After  five  or  ten  minutes  of  artificial  respiration,  it  may  be 
best,  if  in  winter,  to  remove  the  patient  to  a  warm  place. 
During  the  time  of  removal  continue,  if  possible,  artificial 
respiration  and  especially  rhythmic  pressure  in  the  region  of 
the  heart  every  one  or  two  seconds,  since  this  may  tend  to 

*  This  is  necessary  only  when  no  one  else  is  present  to  hold  the 
tongue.  If  two  are  present,  friction  upon  the  limbs  should  also  be  em- 
ployed. 


SUFFOCATION. 


3°9 


keep  the  blood  in  circulation  and  carry  aerated  blood  from 
the  lungs  to  the  tissues. 


FIG.  146.— Showing  position  for  inspiration. 


FIG.  147. — Showing  position  for  expiration. 

Hot  water  applied  to  the  heart  stimulates  its  action,  and 
an  electric  battery,  one  pole  of  the  induction  coil  applied  to 


EMERGENCIES. 

the  back  of  the  neck  and  the  other  to  the  region  of  the  dia- 
phragm, may  also  be  useful  for  this  purpose. 

Warm  water  may  be  injected  into  the  rectum,  100°  F.,  to 
aid  in  restoring  the  heat  of  the  body.  Hot  cloths,  hot  water 
bottles,  hot  bricks,  etc.,  should  also  be  applied  externally  as 
soon  as  possible,  but  burns  should  be  avoided. 

Stimulants  may  be  given  by  the  mouth  if  the  patient  is  able 
to  swallow ;  if  not  and  the  heart  is  still  beating,  they  will,  if 
given  in  the  rectum,  be  absorbed  and  carried  by  the  blood  to 
the  respiratory  and  cardiac  centres. 

Artificial  respiration  should  be  continued  for  one  or  two 
hours  if  necessary,  as  there  is  always  hope  if  the  pulse  or 
heart  beat  can  be  detected.  After  treatment,  avoid  shock  by 
keeping  the  patient  quiet  in  bed  and  use  stimulants  as  freely 
as  needed.  Persons  have  been  saved  after  being  under  water 
as  long  as  twelve  to  fifteen  minutes. 

Choking. — Solid  objects  too  large  to  be  swallowed  or  ac- 
cidentally caught  in  the  larynx  lead  by  their  presence  to  reflex 
spasms  of  the  epiglottis  and  closure  of  the  respiratory  tract. 
The  result  is  a  more  or  less  complete  but  usually  temporary 
suffocation.  Distress  and  violent  coughing  are  prominent 
symptoms. 

Treatment : — Strike  the  patient  strongly  with  the  flat  of 
the  hand  on  the  back.  Lay  him  on  a  bed  or  chairs  with  the 
head  and  upper  part  of  the  chest  hanging  over.  Let  him 
take  a  full  breath  and  then  make  sudden  pressure  on  the  back 
as  he  expires.  In  a  child,  raising  by  the  feet  may  aid  in  dis- 
lodging the  object.  If  ineffective,  do  not  waste  time,  but 
pass  the  finger  down  the  throat,  taking  the  precaution  to  in- 
sert a  folded  handkerchief  between  the  teeth  to  avoid  being 
bitten.  An  ordinary  finger  is  long  enough  to  reach  to  the 
larynx,  and  the  object  may  be  felt  and  removed.  An  emetic 


UNCONSCIOUSNESS.  3  * I 

of  mustard  water  is  sometimes  effective  if  the  object  has  not 
passed  too  far.  Avoid  exhaustion  of  patient  in  the  attempts 
at  removal,  since  objects  which  can  pass  through  the  oesoph- 
agus by  the  larynx  will  do  no  harm  if  they  are  assisted  in 
their  passage  by  masses  of  food  with  large  waste,  as  potato  and 
turnip. 

At  times  children  are  taken  suddenly  with  croup,  the  symp- 
toms of  which  resemble  those  of  choking.  Give  the  child 
warm  water  or,  better,  a  teaspoonful  of  syrup  of  ipecac,  and 
repeat  until  vomiting  occurs.  Apply  hot  water,  ice,  or  mus- 
tard plasters  to  the  throat.  Send  for  the  doctor. 


UNCONSCIOUSNESS. 

Symptoms  and  Treatment. — Unconsciousness  may  be 
caused  by  so  many  conditions  that  it  is  well  to  examine  a 
person  who  is  unconscious  to  determine  the  cause,  if  it  is  not 
known.  The  general  treatment  for  unconsciousness  may  be 
begun  while  the  examination  is  being  made. 

Send  for  a  physician. 

Place  the  patient  on  his  back.  Loosen  the  clothing  about 
throat  and  chest.  Give  him  plenty  of  fresh  air,  and  if  the 
breathing  has  ceased  while  the  pulse  is  still  felt,  apply  arti- 
ficial respiration.  Do  not  give  stimulants  if  the  face  is  flushed 
or  if  the  pulse  is  strong,  since  they  increase  the  heart's  action 
and,  in  case  of  ruptured  blood  vessels  in  the  brain,  the  bleed- 
ing and  consequent  injury  of  the  brain  tissue.  If  the  temper- 
ature of  the  body  is  raised,  apply  wet  cloths  or  ice.  Note  if 
there  is  fracture  of  bones,  including  ribs,  collar  bone,  and 
skull.  Run  the  fingers  down  the  spinous  processes  of  the 
vertebrae  and  note  if  they  are  uniformly  distributed  in  a 


312  EMERGENCIES. 

straight  line.  Open  the  eyes  and  see  if  the  pupils  are  dilated, 
contracted  or  equal  in  size.  Note  odor  of  breath. 

Unconsciousness  may  be  due  to  (a)  narcosis  by  ether, 
chloroform,  opium,  morphine,  chloral,  aconite,  etc.,  the 
treatment  of  which  is  given  under  Poisons,  below  ;  ($)  faint- 
ing; (c)  sunstroke;  (</)  convulsions;  (e)  alcohol  poisoning ; 
(f)  concussion  of  brain  ;  (g)  epileptic  attack;  (h)  apoplexy. 

Fainting. — The  pulse  is  found  weak,  the  face  pale. 

Treatment : — Place  patient  upon  his  back,  with  the  head 
and  chest  lower  than  the  rest  of  the  body.  If  there  is  vom- 
iting, place  him  upon  his  side.  Apply  smelling  salts,  or  give 
ammonia,  strong  coffee,  brandy  or  whiskey.  Insure  plenty 
of  fresh  air  by  fanning,  and  avoid  excitement. 

Sunstroke. — When  working  on  a  hot  sunny  day,  or  on 
warm  days  when  the  air  is  full  of  moisture,  persons  are  some- 
times overcome  with  the  heat,  having  headache,  weakness, 
and  difficulty  of  vision.  The  individual  quickly  becomes  un- 
conscious, and  may  even  fall  so  as  to  be  injured.  The  body 
is  usually  hot  to  the  touch,  the  skin  dry,  the  face  flushed,  the 
pulse  full  and  rapid,  but  there  may  be  coldness,  pallor,  and 
weak  pulse.  Twitchings  of  the  body  may  also  be  noticed. 

Treatment : — Reduce  the  heat  of  the  body  as  rapidly  as 
possible  by  throwing  cold  water  over  the  patient  and  applying 
ice  to  the  head.  Strip  the  body  and  wrap  it  in  a  sheet  kept 
wet  by  frequent  applications  of  water.  Continue  until  con- 
sciousness is  regained  or  the  temperature  of  the  body  is 
lowered.  Do  not  send  the  patient  to  his  home  or  to  a  hos- 
pital until  after  the  treatment  has  been  begun.  If  the  patient 
does  not  exhibit  symptoms  of  high  temperature,  but  shows 
pallor  of  face  and  weak  pulse,  do  not  use  cold  applications, 
but  give  rest,  quiet,  food  and  stimulants  in.  cautious  amounts. 


UNCONSCIOUSNESS.  313 

Convulsions. — Children  may  have  these  attacks  as  a  result 
of  disorders  of  the  stomach,  or  of  fever. 

Treatment : — Keep  the  child  from  injuring  himself.  Put  him 
into  a  warm  bath  or  wrap  him  in  a  blanket  dipped  into  hot 
water.  Keep  the  head  cool  by  applying  cold  water  or  ice. 
If  the  convulsions  continue,  give  an  emetic,  as  a  teaspoonful 
of  syrup  of  ipecac,  if  the  child  can  swallow.  Assist  vomiting 
by  thrusting  the  finger  down  the  throat  or  by  using  a  feather. 
Give  injection  of  soap  and  warm  water,  as  the  seat  of  irritation 
may  be  in  the  lower  bowel. 

Alcoholic  Poisoning — Drunkenness. — The  pulse  is  full  or, 
later,  weak.  The  breathing  is  natural,  the  pupils  of  eyes  of 
equal  size,  and  when  the  eye  is  touched  the  eyelid  will  close 
immediately.  The  patient  can  usually  be  roused  to  speak. 
Alcoholic  odor  in  the  breath  is  always  present,  but  is  not  an 
infallible  symptom.  The  diagnosis  of  intoxication  should  not 
be  made  unless  it  is  an  absolutely  clear  case,  since  many  per- 
sons have  died  from  apoplexy  or  head  injury  when  they  were 
supposed  to  be  drunk. 

Treatment  : — If  the  patient  has  not  already  vomited,  turn 
him  on  his  face  and  raise  him  with  clasped  hands  under  the 
abdomen.  If  not  effective,  give  an  emetic  of  mustard  water. 
If  there  are  symptoms  of  collapse,  as  cold  skin  and  feeble 
pulse,  apply  heat  and  give  stimulants,  as  ammonia,  coffee, 
or  strychnia. 

Concussion  of  Brain. — Unconsciousness  may  be  due  to  a 
blow  on  the  head  which  produces  temporary  unconsciousness, 
or  gives  rise  to  compression  of  the  brain  by  fracture  of  the 
skull  or  by  bleeding  due  to  laceration  of  brain  tissue.  The 
symptoms  are  more  or  less  similar  to  those  of  apoplexy. 
Bleeding  from  the  ear  shows  that  there  has  been  a  fracture  of 
the  base  of  the  skull. 


314  EMERGENCIES. 

Treatment : — Keep  the  patient  in  a  cool  quiet  place,  with 
the  head  slightly  raised.  Avoid  strong  light  and  all  excite- 
ment. Loosen  the  clothing.  If  the  body  is  cold,  apply  heat. 
Do  not  give  stimulants  unless  the  pulse  is  very  weak. 

Epileptic  Attacks  may  come  on  suddenly  or  gradually 
with  symptoms  which  the  patient  recognizes.  Loss  of  con- 
sciousness may  be  accompanied  by  a  peculiar  cry,  sudden 
pallor  of  the  face,  and  more  or  less  stiffening  of  the  body. 
The  tongue  is  sometimes  bitten  and  the  eyes  have  a  peculiar 
upward  rolling  motion.  An  attack  usually  lasts  for  a  minute  or 
two  only,  but  several  attacks  may  follow  each  other  rapidly. 

Treatment : — Keep  patient  from  injuring  himself,  but  do 
not  struggle  with  him.  Allow  him  to  lie  flat,  and  put  a  piece 
of  folded  cloth  between  the  teeth  to  prevent  biting  of  the 
tongue.  The  muscular  contractions  if  prolonged  give  rise  to 
exhaustion  and  lameness,  but  these  may  be  lessened  by  putting 
the  patient  into  a  bath  of  warm  water.  After  the  attack  put 
him  to  bed  and  if  necessary  use  stimulants  in  small  quantities. 

These  attacks  are  seldom  serious,  and  it  is  usually  unneces- 
sary to  do  anything  except  prevent  bodily  injury. 

Apoplexy  is  due  to  bleeding  from  a  ruptured  blood  vessel 
in  the  brain  and  consequent  pressure  of  the  blood  upon  the 
brain  tissue.  The  nerve  cells  or  nerve  fibres  when  pressed 
upon  cease  to  perform  their  functions  and  more  or  less  un- 
consciousness and  paralysis  result.  The  face  is  flushed,  the 
pupils  of  the  eyes  more  or  less  dilated  and  perhaps  unequal 
in  size,  the  breathing  slow,  irregular,  and  noisy,  the  cheeks 
puffed  out  and  drawn  in  with  the  air  movement,  and  the 
pulse  slow  and  full.  There  may  be  also  convulsions  and 
vomiting.  An  important  symptom  is  one-sided  paralysis. 
Notice  whether  the  face  is  drawn  to  one  side  (away  from  the 
paralyzed  side)  or  the  head  kept  on  one  side. 


POISONS.  31$ 

Treatment : — Keep  the  patient  absolutely  quiet,  lying  down, 
the  head  moderately  raised.  Apply  cold  water  or  ice  to  the 
head.  If  the  patient  can  swallow,  give  castor  oil  or  a  dose 
of  salts.  The  bowels  may  be  emptied  by  giving  injection  of 
soap  and  warm  water.  Do  not  give  stimulants. 


POISONS. 

General  Treatment : 

1 )  Send  for  the  nearest  doctor 

2)  Empty  the  stomach  by  the  use  of 

#)   Emetics  to  produce  vomiting  : 

Tickle  throat  with  finger  or  feather. 

Mustard   water,    tablespoonful   to   tumbler  of 
tepid  water. 

Salt  water,  tablespoonful  to  tumbler  of  tepid 
water. 

Zinc  sulphate,  20  to  30  grains  to  half  a  tumbler 
of  tepid  water. 

Copper  sulphate,  i  o  grains  to  2  ounces  of  warm 
water. 

Ipecac,  30  grains  of  powder  or  2  tablespoonfuls 
of  the  wine  or  the  syrup  of  ipecac. 

Caution:  Emetics  are  valueless  when  taken 
after  substances  which  produce  anaesthesia  of 
throat  and  stomach  and  after  powerful  cor- 
rosives (as  opium,  morphine,  carbolic  acid, 
aconite,  cocaine,  strong  acids  and  alkalies), 
have  had  time  to  act. 
£)  Stomach  tube.  Use  any  rubber  tube  two  feet  or 

more  in  length  by  one  half  inch  diameter.      In 

introducing  it,  avoid  the  larynx  and  get  the 


3*6  EMERGENCIES. 

patient  to  make  swallowing  movements.  Meas- 
ure on  the  tube  the  distance  trom  the  stomach 
to  the  mouth  with  the  head  thrown  back,  and 
insert  only  enough  of  the  tube  to  reach  the 
stomach,  so  as  to  avoid  perforation  in  case  of 
corrosion.  Pour  water  through  a  funnel  into 
the  tube ;  then  drop  the  end  of  the  tube  and 
press  upon  the  abdomen  to  force  out  the  con- 
tents of  the  stomach.  This  may  be  repeated 
and  neutralizing  substances  introduced,  alkalies 
for  acids,  acids  for  alkalies. 

3)  Give  antidotes : 

#)   Chemical  (which  destroy  the  power  of  the  poison). 

(See  Special  Poisons.) 
£)   Physiological  (which  neutralize  the  constitutional 

effects  of  the  poison  ;  for  example,  stimulants). 

4)  Give  diluents  (which  dilute  and  hence  weaken  the  power 

of  corrosives,  water,  milk  or  any  harmless  fluid). 

5)  Give  demulcents  (which  tend  to  coat  over  the  poisons, 

or  furnish  a  protective  coating  to  the  stomach,  or  by 
their  coagulation  entangle  the  poison;  for  example, 
milk,  white  of  egg,  boiled  starch,  mucilage,  boiled 
slippery  elm  bark).  These  are  particularly  valuable 
in  the  case  of  corrosive  and  irritant  poisons 
Constitutional  Treatment : 

i)   Stimulants  (which  increase  the  power  of  the  heart  and 
overcome  weakness  and  depression): 
Aromatic  spirits  of  ammonia  or  water  of  ammonia, 

tablespoonful  in  half  glass  of  water ;  frequent  small 

doses. 
Alcohol,  one  or  two  teaspoonfuls  in  two  ounces  of 

water,  or  twice  as  much  whiskey  or  brandy. 


COMMON  POISONS  4ND   THEIR  ANTIDOTES.       3*7 

Coffee,  in  strong  solution. 

Vapor  of  ether  inhaled  or  one  teaspoonful  in  cold 

water. 
Tincture  of  nux  vomica,  five  to  ten  drops  in  water  ; 

or  strychnia  ^  to  -fa  grain. 
Stimulants   are    not   absorbed  from   the    stomach  if 

there   is  much  corrosive  action,  as  in  the  case  01 

strong  acids  and  alkalies ;  they  may  then  be  given 

by  the  rectum. 

2)  External  heat  (of  special  value  in  depression). 

Apply  warm  blankets,  hot  water  bottles,  hot  bricks, 

etc. 
Caution :    In  case  of  more  or  less  complete  loss  of 

consciousness,  apply  nothing  hot  enough  to  burn. 

3)  Friction  (to  aid  depressed  circulation). 

Rub  toward  the  heart  in  order  to  aid  the  venous  re- 
turn. Keep  the  patient  in  a  horizontal  position, 
or,  in  case  of  profound  depression,  with  the  head 
and  chest  lower  than  the  rest  of  the  body.  Sud- 
den raising  of  the  head  should  always  be  avoided. 


COMMON  POISONS  AND  THEIR  ANTIDOTES. 

Irritant  Poisons  (more  or  less  corrosive)  : 

Arsenic   (paris  green,  Fowler's   solution,  arsenious  acid, 
.    some  vermin  killers). 

Precipitated  oxide  of  iron,  made  by  precipitating  any 
solution  of  iron  with  ammonia,  washing  soda  or  any 
strong  alkali  in  solution.  Wash  precipitate  with 
water  through  a  cloth.  Give  two  or  three  tablespoon- 


EMERGENCIES. 

fuls.  If  the  iron  precipitate  cannot  be  obtained 
immediately,  give  moistened  plaster  of  wall  which  will 
mix  with  the  poison  and  serve  to  protect  the  stomach. 
Wash  out  stomach. 

Phosphorus  (matches,  Rough  on  Rats). 
Emetics :   magnesia,  plaster  from  wall. 
Empty  stomach. 

Caution:  Do  not  give  oily  substances  as  milk,  etc. 
Corrosive  sublimate  (mercuric  bichloride,  bug  poison). 

White  of  egg ;  emetics.     Wash  out  stomach. 
Iodine  (tincture). 
Starch  (boiled). 
Lead  (paints,  hair  dyes). 

Sulphates  (Epsom  salts,  Glauber's  salts,  alum),  emetics, 

etc. 

Cantharides  (Spanish  fly,  irritant  liniments). 
Demulcents,  diluents,  camphor,  and  opium. 
Caution:  Avoid  fat  or  oil. 
Corrosives : 

Acids  [sulphuric  acid  =  oil  of  vitriol  (H2SO4);  hydrochloric 
acid  —  muriatic  acid  (HC1);  nitric  acid  (HNO3)]. 
Water,  dilute  alkalies,  lime  water,  soap  solution,  tooth 
powder,  chalk  or  plaster  of  wall,  followed  by  demul- 
cents.     Wash  out  stomach. 
Carbolic  acid. 

Water,  sulphates  (Glauber's   or  Epsom  salts)  or  alum. 
Roll  patient  to  prevent  corrosive  action.     Wash  out 
stomach. 
Oxalic  acid. 

Lime    or    chalk.      Stimulants    as    needed.     Wash    out 

stomach. 
Alkalies  [caustic  soda  =  sodium  hydroxide  (NaOH);  caustic 


COMMON   POISONS  AND   THEIR  ANTIDOTES. 

potash  =  potassium  hydroxide  (KOH);  ammonia  =  am- 
monium hydroxide  (NH4OH)] . 

Dilute  acid,  vinegar,    hard  cider,    lemon  or  orange 

juice,  followed  by  demulcents. 
Narcotics : 

Opium  (laudanum,  paregoric,  morphine,  black  drops, 
McMunn's  elixir,  soothing  syrups,  cholera  mixtures, 
Dover's  powder). 

Solution  'potassium  permanganate,  10  to  15  grains  in  half 
a  glass  of  water.  Wash  out  stomach.  Tannic  acid, 
strong  hot  coffee,  strychnia,  -fa  to  TV  grain. 
Electric  battery.  Keep  awake  by  non -exhausting 
means.  Perform  artificial  respiration  and  maintain 
body  temperature. 

In   opium  poisoning  a  distinguishing  symptom  is 
pin-head  contraction  of  the  pupils  of  the  eyes. 
Chloral  hydrate  (chloral,  knock-out  drops). 

Treatment  same  as  for  opium,  except,  keep  quiet,  head 

low,  give  ammonia,  or  other  stimulants. 
Aconite. 

Wash   out   stomach.     Stimulants,   as   coffee,   ammonia, 

alcohol. 
Tobacco  (snuff). 

Tea    or    coffee,    vinegar,   and    stimulants.      Heat    and 

friction. 
Ether  and  chloroform. 

Lower    head  -  and    chest.     Use    artificial     respiration. 
Stimulants,     especially    ammonia,     nux    vomica     or 
strychnia. 
Nux  vomica  (strychnia). 

Vapor  of  ether  or  chloroform,  to  control  the  spasms. 
Bromide  of  potassium  or  sodium  (20  to  30  grains), 


320  EMERGENCIES. 

chloral  (20  grains)  or  morphine  (£  to  -J  grain).     Give 
in  rectum  if  patient  cannot  swallow. 


FIRST  AID  TO  THE   INJURED. 

Dislocations. — When  the  end  of  a  bone  slips  out  of  its 
joint,  it  is  said  to  be  dislocated.  Owing  to  the  arrangement 
of  ligaments,  dislocation  is  associated  with  more  or  less  tear- 
ing of  the  capsular  and  reinforcing  ligaments  and  bleeding 
from  the  ruptured  vessels,  followed  by  swelling  and  discolora- 
tion. The  swelling  of  the  joint  is  apt  to  be  so  great  that  it  is 
wise  to  restore  the  bone  as  soon  as  possible.  Compare  it 
with  its  corresponding  joint  and  attempt  to  restore  it  to  its 
place ;  if  successful  apply  a  bandage,  handkerchief  or  cloth 
in  such  a  way  as  to  keep  the  joint  in  place.  It  is  well  if  the 
joint  is  accessible,  as  the  ankle,  elbow,  etc. ,  to  apply  a  wad 
of  cloth  or  other  soft  elastic  material  (compress)  around  the 
joint  and  then  wind  a  bandage  tightly  over  it  to  prevent 
swelling. 

Fractures. — A  fracture  or  break  of  a  bone  may  usually  be 
recognized  by  movement  of  the  pieces  or  by  crepitus  when  the 
broken  ends  are  rubbed  together.  The  pieces  of  bone  should 
be  brought  as  nearly  as  possible  into  their  proper  positions 
and  held  there  by  splints.  Sticks,  umbrellas,  canes,  pillows 
or  folded  sheets  may  be  fastened  with  cords  or  bandages 
along  the  sides  of  the  limb  to  stiffen  it  and  hold  it  in  position. 
To  move  such  a  patient  it  is  necessary  to  put  him  on  a  board, 
shutter  or  other  object  so  that  he  can  lie  at  full  length  and  be 
carried  without  jarring.  An  arm  may  be  put  into  a  sling 
passed  around  the  neck.  A  broken  leg  may  be  bound  to  the 
sound  one,  taking  care  to  draw  the  foot  of  the  broken  leg  out 
to  the  full  length  of  the  sound  one. 


FIRST  AID  TO   THE  INJURED. 


321 


Bleeding. — Either  arteries  or  veins  may  be  cut  and  the 
blood  thus  permitted  to  escape.  Arterial  blood  is  recognized 
by  its  spurting.  Venous  bleeding  is  usually  a  slow  oozing. 
In  case  an  artery  is  injured,  it  is  not  sufficient  to  apply  a 
bandage  over  the  point  of  injury,  but  the  artery  must  be 
compressed  at  some  point  where  it  lies  over  a  bone  so  that 
the  pressure  may  be  sufficient  to  close  it  against  the  blood 
pressure.  Pressure  may  be  applied  by  means  of  a  pad  of 


FIG.  148. — Compression  of  femoral  artery.         FIG.  149. — Compression  of  artery  in 

arm. 

cloth,  a  smooth  stone  or  other  object  bound  tightly  over  the 
spot.  The  chief  points  of  pressure  for  arteries  are  as  follows  : 
i)  behind  the  knees;  2)  the  inner  side  of  the  thigh  (Fig. 
148) ;  3)  the  inner  border  of  the  biceps  muscle  in  the  upper 
arm  (Fig.  149). 

For  bleeding  from  veins  and  ordinary  slight  cuts,  a  light 
pressure  by  a  pad  over  the  point  of  injury  is  sufficient. 


2^2  EMERGENCIES. 

Bleeding  from  the  nose  suggests  trouble  with  the  mucous 
membrane  lining  the  nasal  cavity,  and  if  habitual  should  re- 
ceive the  attention  of  a  physician.  Profuse  bleeding  may 
necessitate  the  application  of  dilute  solutions  of  tannin  or 
alum  ;  if  these  are  not  successful,  the  nose  should  be  plugged 
by  a  physician. 

Bleeding  from  the  lungs  and  stomach  occurs  at  times,  but 
is  seldom  fatal.  Rest  and  quiet  are  essential. 

Bruises  and  Sprains. — Apply  hot  water  or  rub  vigorously 
with  fingers. 

Antiseptic  Treatment  of  Wounds. — "Catching  cold"  in 
a  wound  means  the  entrance  of  bacteria  and  consequent  in- 
flammation. After  carefully  washing  the  hands  with  soap 
and  hot  water,  wash  the  wound  thoroughly  with  a  solution  of 
carbolic  acid  (3$),  a  solution  of  corrosive  sublimate  (i  to 
1000),  or  a  solution  of  formalin  (i  to  40).  If  you  do  not 
have  these,  use  strong  alcohol,  whiskey,  brandy  or  boiled 
water.  Then  bring  the  edges  of  the  wound  together,  hold 
in  place  by  a  compress  of  baked  clean  cloth,  and  bind  tightly 
with  a  bandage.  If  treated  in  this  way,  the  wound  will  ordi- 
narily heal  "  by  first  intention,"  and  need  not  be  disturbed. 

Burns  and  Scalds. — If  slight,  apply  a  paste  of  cooking 
soda  or  alum.  If  extensive,  apply  Carron  oil  (equal  parts 
lime  water  and  linseed  oil).  When  a  burn  covers  a  quarter 
of  the  surface  of  the  body,  it  should  be  regarded  as  very 
serious,  possibly  fatal,  and  a  physician  should  be  summoned 
immediately.  Apply  vaseline,  Carron  oil,  etc.,  or  put  into 
bath  tub  with  warm  water  to  which  a  cup  or  two  of  salt  has 
been  added.  Keep  the  water  at  a  temperature  of  90°  to 
100°  F.  Watch  the  strength  carefully  and  give  stimulants,  as 
strychnia,  coffee,  alcohol,  ammonia,  etc.,  as  needed.* 

*  When  a  person's  clothing  takes  fire,  roll  him  in  wet  cloths,  woollen 


FIRST  AID   TO   THE  INJURED.  323 

Pain. — Apply  heat,  as  hot  water  bottle,  etc.,  or  mustard 
plaster. 

Stings  of  Insects. — Apply  ammonia  or  soda. 

Snake  Bite. — Do  not  give  large  amounts  of  alcohol.  Suck 
out  the  poison,  or  tie  a  string  tightly  around  the  limb  above  the 
point  of  injury  to  prevent  carrying  the  poison  into  the  system, 
and  cut  the  wound  freely  with  sharp  knife  to  cause  bleeding. 
Use  stimulants,  as  ammonia,  coffee,  alcohol,  if  necessary. 

Poisoning  by  Canned  Foods,  Ice  Cream,  Salads,  etc.— 
Give  an  emetic,  and  castor  oil  to  clear  out  bowels. 

Foreign  Body  in  Eye. — Take  a  small  pencil  or  stick  and 
press  upon  the  middle  of  the  upper  part  of  the  eyelid,  at  the 
same  time  raising  the  lid  by  means  of  the  eyelashes  with  the 
other  hand.  Press  down  the  cartilage  of  the  lid  until  its 
edge  swings  below  and  exposes  the  inner  surface.  Find  the 
object  and  remove  by  making  a  soft  moistened  point  of  a 
handkerchief.  When  no  assistance  can  be  obtained  avoid 
rubbing  the  eye,  grasp  the  eyelashes  and  hold  away  from  the 
eye  to  permit  the  tears  to  wash  the  object  from  beneath. 
One  or  two  drops  of  a  2%  solution  of  cocaine  may  be  put 
into  the  eye  to  allay  the  pain  after  the  object  is  removed  or 
the  pain  of  an  object  which  cannot  be  removed.  Persistent 
aching  and  redness  of  one  eye  usually  means  irritation  by  a 
foreign  body. 

Frost  Bite. — When  a  part  of  the  body  is  frozen  it  should 
be  rubbed  with  melting  snow,  ice  or  ice  water.  As  soon  as 
the  blood  returns  apply  cracked  ice  to  reduce  the  reaction. 

clothing,  rug  or  carpet,  or  put  out  the  fire  with  water,  sand,  ashes  or 
other  non-burnable  material.  If  nothing  is  at  hand,  pull  off  burning 
clothing  or  roll  him  over  and  over  to  crush  out  the  flame.  When  in  a 
burning  building  where  the  smoke  is  thick,  k.eep  the  head  near  the  floor. 
If  no  escape  is  possible,  get  upon  the  outside  of  the  window-sill  and  clos* 
the  window. 


324  EMERGENCIES. 

Contagious  Diseases. — Since  contagious  diseases  are  all 
probably  due  to  bacteria,  washing  serves  to  remove  them  from 
the  person,  and  hence  aids  to  avoid  infection.  When  one 
comes  in  contact  with  a  sick  person  he  should  touch  him 
only  with  the  hands  and  then  wash  them  with  warm  water  and 
soap  immediately  afterward,  to  avoid  contaminating  door 
knobs  and  articles  of  furniture  which  others  are  liable  to 
touch.  It  is  better  to  try  to  avoid  all  diseases,  even  whooping 
cough,  measles  and  mumps,  since  they  are  never  without 
possibilities  of  danger. 

Tuberculosis  (  consumption  j  must  be  considered  as  one  of 
the  contagious  diseases  and  should  be  guarded  against  by 
isolation  or  rigid  cleanliness,  including  the  destruction  of  all 
sputum  by  burning  or  with  strong  antiseptics. 

A  person  who  has  a  contagious  disease  should  be  immedi- 
ately isolated  from  every  one  except  a  nurse,  and  the  nurse 
should  also  be  isolated.  All  articles  of  food  or  clothing 
coming  from  the  room  should  be  burned  or  disinfected. 

Most  contagious  diseases  are  acquired  by  transferring  the 
bacteria  from  objects  on  which  they  have  been  deposited  to 
the  mouth,  by  taking  infected  food,  as  milk  or  water,  or  by 
inhaling  them  as  dust.  All  suspicious  food  and  water  should 
be  well  cooked  or  boiled  before  it  is  used. 

Disinfection. — All  unnecessary  articles  of  furniture,  dra- 
peries, cushions,  etc.,  should  be  removed  from  a  room  to  be 
occupied  by  a  person  with  a  contagious  disease.  Articles  of 
furniture  and  clothing  which  have  come  in  contact  with  the 
patient  directly  or  indirectly  should  be  either  destroyed  by 
burning,  or  disinfected  by  boiling,  or  soaking  thoroughly  in 
a  strong  antiseptic  solution,  such  as  carbolic  acid  or  formalin. 
The  room  should  be  disinfected  by  the  fumes  of  formalde- 
hyde generated  from  a  solution  of  formalin  (one  liter  of 


FIRST  AID   TO   THE  INJURED.  32S 

formalin   to    1000   cubic   feet   of  air  space).     Windows  and 

doors  should  be  tightly  closed  and  sealed. 

Disinfectant  Solutions : 

Milk  of  lime — one  part  of  fresh  lime  to  five  parts  of  water. 
Stir  before  using.  This  may  be  used  for  discharges  in 
typhoid,  cholera,  etc.,  and  should  be  mixed  with  them 
in  sufficient  amount  to  make  them  strongly  alkaline. 
After  standing  a  half  hour  they  may  be  thrown  into 
privy  or  sewer.  Whitewashing  with  a  freshly  made 
solution  is  an  effective  treatment  for  nearly  all  forms  of 
bacteria. 
Chloride  of  lime — one  pound  to  two  and  one  half  gallons 

of  water.  This  may  be  used  for  excreta. 
Fumigation  by  sulphur  is  comparatively  valueless.  Sun- 
light is  effective  for  surface  disinfection  only.  Ventila- 
tion cannot  remove  all  disease  germs.  Dusting  and 
beating  of  garments  merely  serve  to  scatter  the  germs 
and  endanger  the  individual  who  does  the  beating. 


APPENDIX  B. 

THE  ACTION  OF  ALCOHOL  AND  TOBACCO  UPON  THE 
HUMAN  BODY. 

Introductory. — We  have  already  seen  (p.  98)  that  alcohol 
is  not  to  be  regarded  as  either  a  tissue-forming  or  a  force- 
giving  food. 

By  causing  a  transference  of  heat  from  internal  parts  to 
the  skin,  in  which  the  main  organs  of  the  temperature  sense 
(p.  283)  are  located,  it  produces  a  temporary  feeling  that  the 
body  is  warmer ;  but  the  final  result  is  a  loss  of  animal  heat 
to  the  air,  and  a  decrease  of  the  temperature  of  the  body  as  a 
whole.  Experiments  made  on  men  under  military  regimen 
and  discipline  have  proved  that  alcohol  does  not  increase  the 
power  of  sustained  muscular  work,  though  it  may  for  a  brief 
time  stimulate  to  unhealthy  activity.  The  relative  amount  of 
energy  liberated  in  the  body  for  its  own  use  may  be  very  fairly 
calculated  by  comparing  the  amount  of  oxygen  absorbed  by 
the  lungs  on  one  day  with  the  amount  absorbed  on  another. 
We  have  learned  that  on  the  days  when  alcohol  is  taken  the 
oxygen  absorbed  is  not  increased.  Alcohol  seizes  some  of 
the  oxygen  which  the  foods  and  tissues  would  have  utilized  in 
its  absence;  and  what  it  takes  they  lose.  Most  authorities 
even  maintain  that  alcohol  prevents  oxidation,  and  therefore 
tissue  activity,  indirectly  as  well  as  directly;  these  experi- 

327 


ALCOHOL  4riD   TOBACCO. 

menters  find  that  it  not  only  takes  oxygen  from  the  tissues, 
but  so  influences  them  as  to  diminish  their  power  of  using 
what  it  leaves.  We  may  conclude  that  under  ordinary  cir- 
cumstances alcohol  is  of  no  use  as  an  energy-yielding  food ; 
although,  since  it  is  oxidized  in  the  body,  it  would  act  as  a 
real  food  to  a  starving  man ;  or  to  a  very  sick  person  who 
might  be  unable  for  the  moment  to  absorb  and  digest  other 
substances. 

As  regards  tissue-formation,  alcohol  cannot  build  up  proteid 
material,  since  it  contains  no  nitrogen ;  and  proteid  material 
constitutes  the  essential  part  of  muscular,  glandular,  and 
nervous  tissues.  There  is  even  some  evidence  that  alcohol 
leads  to  excessive  waste  of  such  tissues :  several  competent 
observers  have  found  that  its  use  increases  the  amount  of 
nitrogen  waste  excreted  from  the  body.  The  only  tissues 
whose  formation  alcohol  seems  sometimes  to  increase  are 
fatty  and  connective  tissues ;  and  we  shall  presently  learn  that 
in  most  cases  the  superabundance  of  these  tissues  is  deposited 
in  places  where  it  does  harm. 

The  study  of  alcohol  as  an  article  of  diet  leads  therefore  to 
the  result  that  (though  a  physician  may  find  it  useful  as  a 
medicine  in  a  crisis  of  disease  when  the  system  needs  urging 
to  make  a  special  effort)  it  cannot  fairly  be  regarded  as  a  food 
when  taken  by  persons  in  good  health  and  properly  nourished. 

The  whip  applied  to  a  horse  will  arouse  him  to  call  on  his 
reserve  force,  and  perhaps  carry  himself  and  his  rider  safely 
past  some  point  of  special  danger ;  but  it  does  not  in  any  way 
nourish  the  horse.  As  regards  the  healthy  human  body 
alcohol  may  be  compared  to  a  whip  :  an  amount  of  it  not 
sufficient  to  cause  drunken  sleep,  temporarily  excites  various 
organs  ;  but  the  consequence  is  subsequent  greater  exhaustion. 

So  far  we  have  learned  that  alcohol  as  a  regular  article  of 


ALCOHOLIC  BEVERAGES.  329 

diet  is,  at  least,  useless.  Were  that  all,  we  might  regret  the 
annual  waste  of  corn,  barley,  wheat,  and  fruits  in  its  produc- 
tion, and  think  the  man  foolish  who  spent  his  money  on  it. 
In  such  case  the  matter  would  be  one  for  moralists  and 
political  economists  to  deal  with,  and  physiologists  and 
students  of  hygiene  might  leave  it  alone.  Unfortunately, 
alcoholic  drinks  are  not  merely  useless  but  positively  hurtful, 
when  taken  regularly,  even  in  what  is  usually  called  modera- 
tion. Alcohol  has  probably  caused  in  the  past,  and  is 
certainly  causing  at  present  in  civilized  nations,  more  disease 
and  death  than  either  bad  drainage,  bad  ventilation,  over- 
crowding, deficient  food,  overwork,  or  any  other  of  the  con- 
ditions prejudicial  to  health  concerning  which  Physiology  and 
Hygiene  warn  us.  The  moral  degradation  and  the  physical 
condition  of  the  drunkard  speak  for  themselves ;  it  is  there- 
fore the  more  insidious  consequences  of  alcohol-drinking  that 
we  shall  mainly  describe. 

Alcohol,  when  pure,  is  a  transparent  colorless  liquid,  con- 
taining the  elements  carbon,  hydrogen,  and  oxygen  (C2H6O); 
it  is  lighter  than  water,  and  boils  at  a  considerably  lower 
temperature ;  is  highly  inflammable,  burning  with  a  bluish 
flame  ;  and  is  the  essential  constituent  of  all  fermented  liquors 
in  common  use. 

Alcoholic  Beverages  include  (i)  malt  liquors,  as  beer,  ale, 
stout,  and  porter;  (2)  cider  and  perry /  (3)  wines,  as  claret, 
sherry,  port,  champagne,  and  catawba ;  (4)  distilled  spirits,  as 
brandy,  rum,  and  whiskey ;  and  their  compounds,  as  gin, 
cherry  brandy,  pineapple  rum,  and  so  forth;  (5)  liqueurs, 
made  by  adding  various  flavoring  essences  to  different  kinds 
of  spirits.  All  contain  alcohol  in  greater  or  less  proportion, 
varying  from  over  70  volumes  in  the  100  in  some  kinds  of 
rum  to  less  than  2  in  the  100  in  "small"  beer. 


33°  ALCOHOL  AND   TOBACCO. 

The  Direct  Physiological  Action  of  Pure  Alcohol. — Pure 
alcohol  is  a  very  expensive  substance,  mainly  employed  in 
chemical  experiments  and  in  the  manufacture  of  certain  per- 
fumes and  essences.  However,  some  clues  to  the  action  of 
diluted  alcohol  on  the  body  may  be  obtained  by  a  study  of  its 
action  in  the  concentrated  form. 

Strong  alcohol  having  a  great  tendency  to  combine  with 
water,  rapidly  extracts  that  substance  from  any  animal  organ 
placed  in  contact  with  it ;  as  is  shown  by  the  hardening  and 
shrivelling  of  museum  specimens  placed  in  it. 

Added  to  raw  white  of  egg  it  coagulates  it,  much  as  if  the 
egg  had  been  boiled :  added  to  fresh  blood  it  acts  in  a  simi- 
lar manner,  coagulating  the  serum  albumin  as  heat  does 

(P-  155)- 

Pure  alcohol  placed  on  the  skin  evaporates  very  rapidly, 
and  in  so  doing  abstracts  heat  (p.  226,  no/e),  producing  a 
sensation  of  coolness.  This  is  succeeded  by  a  feeling  of 
warmth  in  the  part,  which  also  becomes  red  from  temporary 
paralysis  of  its  blood  vessels,  causing  them  to  dilate.  If  the 
evaporation  be  prevented,  as  by  putting  a  little  alcohol  on 
the  skin  and  covering  it  with  a  thimble,  the  alcohol  acts  as 
an  irritant ;  it  causes  smarting,  and  finally  sets  up  inflamma- 
tion. 

On  mucous  membranes  alcohol  acts  much  as  on  the  skin, 
but  its  irritant  effect  is  more  marked.  Placed  on  the  tongue 
it  causes  a  feeling  of  coolness,  followed  by  a  hot,  biting  sen- 
sation, and  a  red  congested  condition  of  the  area  with  which 
it  came  in  contact.  Introduced  into  the  stomach  of  a  rabbit 
or  dog,  where  it  cannot  readily  evaporate,  strong  alcohol 
causes  congestion  and  inflammation  varying  in  intensity  with 
its  amount.  If  the  dose  is  large  the  animal  dies  almost 
instantly,  because  the  powerfully  irritated  sensory  nerves  of 


DILUTED  ALCOHOL— ABSORPTION  OF  ALCOHOL      33 1 

the  gastric  mucous  membranes  reflexly  excite  a  nerve  centre 
which  stops  the  heart's  beat. 

Diluted  Alcohol  does  not  produce  the  above-described 
direct  actions  of  the  pure  liquid  :  this  latter  taken  into  the 
stomach  acts  as  a  powerful  irritant  poison,  and  generally 
produces  its  main  effects  on  the  stomach  itself.  Alcohol  in 
such  proportion  as  it  exists  in  most  alcoholic  drinks  exerts 
much  less  local  action  on  the  gastric  mucous  membrane ;  but 
it  is  absorbed  and  carried  in  the  blood  and  lymph  through 
the  body,  and  if  steadily  taken  day  after  day  acts  upon  and 
alters  for  the  worse  nearly  every  important  organ.  The 
organ  first  or  most  seriously  attacked  varies  with  the  form  in 
which  the  alcohol  is  taken,  with  the  amount  consumed  daily, 
and  with  the  constitution  of  the  individual.  Probably  no 
one  individual  ever  suffered  from  all  the  diseased  states 
produced  by  alcohol  described  in  the  following  pages ;  but 
habitual  drinkers  are  very  apt  to  experience  one  or  more  of 
them.  The  diseases  produced  by  alcohol  after  absorption 
into  the  blood  come  on  so  gradually  (except  in  the  case  of 
obvious  drunkards)  that  the  victim  rarely  perceives  them 
until  serious  if  not  irremediable  damage  has  been  done : 
indeed,  physicians  have  only  recently  come  to  clearly 
recognize  that  men  who  in  common  phrase  "were  never  in 
their  lives  under  the  influence  of  liquor  ' '  may  nevertheless 
be  drinking  enough  to  do  them  grave  injury. 

Absorption  of  Alcohol. — When  alcohol  (so  diluted  as  not 
to  cause  active  inflammation  of  the  stomach)  is  swallowed,  it 
is  quickly  absorbed  by  the  capillary  blood  vessels  of  the 
gastric  mucous  membrane.*  These  pass  it  on  to  the  portal 

*  An  exception  to  the  rapid  absorption  of  alcohol  sometimes  occurs 
when  a  large  quantity  of  raw  spirits  is  taken.  Many  cases  are  recorded 
where  men  have  for  a  wager  drunk  a  bottle  of  whiskey  or  brandy.  The 


332          ALCOHOL  AND  TOBACCO. 

vein,  which  carries  it  (p.  177)  direct  to  the  liver.  Collected 
from  the  liver  by  the  hepatic  veins,  it  is  conveyed  through 
the  inferior  vena  cava  to  the  right  auricle  of  the  heart. 
Thence  it  passes  on  in  the  general  blood  flow  (pp.  167,  168, 
177)  to  right  ventricle,  lungs,  left  auricle,  left  ventricle, 
aorta,  and  by  branches  of  the  aorta  to  the  body  in  general : 
to  the  heart  muscle  (by  the  coronary  arteries,  p.  169),  to  the 
brain  and  spinal  cord,  to  *he  muscles,  to  the  kidneys,  to  the 
skin.  We  have  to  study  its  action  on  all  these  organs. 

The  Primary  Effects  of  a  Moderate  Dose  of  Diluted 
Alcohol,  as  a  glass  of  whiskey  and  water,  on  one  unaccustomed 
to  it,  are  to  cause  temporary  congestion  of  the  stomach ; 
dilatation  of  blood  vessels  of  the  skin,  indicated  by  the 
flushed  face ;  a  more  rapid  and  forcible  beat  of  the  heart ;  * 
nervous  excitement,  exhibited  by  restlessness  and  talkative- 
ness. Then  some  incoherence  of  ideas,  and  often  giddiness. 
Finally  there  is  a  tendency  to  sleep.  On  awaking  the  person 
has  some  feeling  of  depression,  not  much  appetite,  and  is  in 
general  a  little  out  of  sorts  for  a  day. 

If  the  dose  be  larger  the  stage  of  giddiness  is  accompanied 
by  diminution  of  the  sensibility  of  the  skin,  and  imperfect 
control  over  the  voluntary  muscles,  indicated  by  defective 
articulation  and  a  staggering  gait.  The  muscles  moving  the 
eyeballs  cease  to  work  in  harmony.  Normally  they  act 
unconsciously,  turning  the  eyes  so  that  images  of  objects 
looked  at  are  focused  on  corresponding  points  of  the  retinas, 
and  objects  are  seen  single.  Soon  after  the  voluntary  move- 
result  is  often  sudden  death,  but  sometimes  no  effect  is  noticed  for  fifteen 
or  twenty  minutes  ;  then  there  is  a  sudden  unconsciousness,  passing  into 
stupor,  which  ends  in  death.  In  such  cases  the  large  quantity  of  strong 
spirits  seems  temporarily  to  paralyze  the  absorbing  power  of  the  stomach. 

*It  is  doubtful  if  chemically  pure  alcohol  diluted  with  water  quickens 
the  pulse  ;  most  ordinary  alcoholic  beverages,  however,  undoubtedly  do. 


SECONDARY  EFFECTS  OF  ALCOHOL  333 

ments  are  affected  the  involuntary  regulation  of  the  eye- 
muscles  is  impaired,  and  objects  are  seen  double,  the  eye- 
balls being  no  longer  so  turned  as  to  bring  images  on 
corresponding  retinal  points.  The  stomach  may  also  be  so 
irritated  as  to  lead  to  vomiting.  Then  comes  deep  drunken 
sleep ;  followed  by  headache,  loss  of  appetite,  and  prostration 
similar  to,  but  more  marked  than,  that  occurring  after  the 
smaller  dose. 

If  the  alcoholic  indulgence  be  repeated,  day  after  day, 
some  of  the  above -described  primary  consequences  become 
less  marked ;  but  they  give  way  to  more  serious  functional 
and  structural  diseases. 

The  Secondary  Effects  of  Alcohol  vary  much  in  intensity 
with  the  form  in  which  it  is  taken ;  also,  no  doubt,  with  the 
constitution  of  the  person  taking  it,  and  with  the  length  of 
time  during  which  he  has  been  drinking.  We  shall  consider 
them  in  three  groups  :  I.  Comparatively  slight  and  curable 
diseased  states  due  to  what  is  commonly  considered  moderate 
drinking.  II.  Severe  acute  alcoholic  diseases.  III.  Chronic 
and  usually  incurable  morbid  states,  due  to  steady,  prolonged 
drinking ;  these  fall  into  three  main  subdivisions  :  a.  Gen- 
eral tissue  deterioration ;  b.  Destruction,  more  or  less  com- 
plete, of  certain  organs ;  c.  Deterioration  of  mind  and 
character. 

I.  Minor  Diseased  Conditions  produced  by  Moderate 
Drinking. — Of  these,  alcoholic  dyspepsia  is  the  most  frequent. 
A  vast  number  of  persons  suffer  from  it  without  knowing  its 
cause,  people  who  were  never  drunk  in  their  lives,  and  con- 
sider themselves  very  temperate.  "  The  symptoms  vary,  but 
when  slight  are  something  like  these  :  A  man  (or  woman) 
complains  of  slight  loss  of  appetite,  especially  in  the  morning 
for  breakfast  •  feels  languid  either  on  rising  or  early  in  the 


334  ALCOHOL  AND   TOBACCO. 

day ;  retches  a  little  in  the  morning,  and  perhaps  brings  up  a 
little  phlegm  only,  or  may  actually  vomit ;  or  may  be  able  to 
take  breakfast,  but  feels  sick  after  it.  Towards  the  middle  of 
the  morning  he  is  heavy  and  languid,  perhaps,  and  does  not 
feel  easy  until  he  has  had  a  glass  of  sherry  or  some  spirits  ; 
then  gets  on  pretty  well,  and  can  eat  lunch  or  dinner.  Or 
if  worse,  the  appetite  for  both  is  defective,  and  there  is 
undue  weight  or  discomfort  after  meals.  .  .  .  Now  all 
these  symptoms  may  be  due  to  other  causes,  but  when  taken 
together  they  are  by  far  most  commonly  due  to  alcohol. ' '  * 

Another  frequent  result  of  regular  "moderate"  drinking 
is  tremor,  or  shakiness  of  the  hands.  The  hand  is  unsteady 
when  the  arm  is  folded,  and  is  seen  to  tremble  if  it  be  held 
out  with  the  arm  extended.  This  tremor  is  very  marked  in 
the  alcoholic  disease  known  as  delirium  tremens  (p.  335). 
Even  in  its  simple  form  it  interferes  with  the  performance 
of  any  action  calling  for  manual  dexterity.  The  trembling 
may,  in  most  cases,  be  stopped  for  a  time  by  an  extra  glass ; 
and  thus  often  leads  to  the  acquirement  of  more  serious 
diseases. 

We  class  the  above  as  minor  diseased  conditions,  because 
in  most  cases  they  occur  before  the  will  power  is  seriously 
impaired,  and  abstinence  from  alcohol  is  soon  followed  by 
recovery. 

II.  Acute  Alcoholic  Diseases. — A  single  large  dose  of 
alcohol,  or  the  repetition  of  small  doses  at  short  intervals, 
ends  in  a  fit  of  drunkenness. 

The  disgusting  appearance  of  a  drunken  man,  the  loathing 

which  he  excites  even  in  those  most  attached  to  him,  the  loss 

of  control  over  his  actions,  which  makes  him  the  prey  of 

criminals,  or,  yet  worse,  a  criminal  himself,  taken  together 

*Dr.  Greenfield,  in  "Alcohol :  its  Use  and  Abuse." 


DELIRIUM   TREMENS— DIPSOMANIA.  335 

make  a  picture  to  which  the  physiologist  need  add  nothing. 
A  man  not  deterred  by  its  contemplation  will  not  be  hindered 
in  the  indulgence  of  his  appetite  by  any  argument  based  on 
injury  to  his  health. 

Delirium  Tremens. — Repeated  drunkenness  usually  ends 
in  an  attack  of  delirium  Iremens,  but  this  disease  is  more 
frequently  the  result  of  prolonged  drinking  which  has  never 
culminated  in  actual  drunkenness.  It  is  especially  apt  to 
occur  in  ' '  those  who  drink  hard,  but  keep  from  actual  loss  of 
consciousness,  especially  those  engaged  in  hard  mental  work 
or  subjected  to  great  moral  strain  or  shock ;  and,  too,  those 
of  certain  temperaments  are  peculiarly  liable  to  it.  It  is 
preceded,  usually,  by  loss  of  sleep,  ideas  of  persecution  or 
injury,  with  no  foundation  in  fact,  and  slight  hallucinations, 
especially  at  night ;  the  man,  meanwhile,  in  the  day  looking 
anxious,  slightly  excited,  nervous  and  tremulous,  and  perhaps 
narrating  as  actual  occurrences  the  hallucinations  of  the  pre- 
ceding night.  Then  the  senses  are  partly  lost ;  he  sees  spec- 
tres, horrible  and  foul  creatures  about  him ;  has  all  sorts  of 
painful,  terrifying  visions  (whence  the  common  name  of  the 
'  horrors  ' ) ;  is  extremely  tremulous,  and  either  excited  or  lies 
prostrate,  trembling  violently  on  movement,  sleepless,  anx- 
ious, and  a  prey  to  spectres  and  terrors  of  the  imagina- 
tion." * 

Few  persons  die  in  their  first  attack  of  delirium  tremens, 
but  it  is  nature's  unmistakable  warning  to  the  tippler;  let 
him  not  disregard  it,  unless  he  is  prepared  to  die  without 
hope  in  maniacal  imaginings  so  frightful  that  those  around 
his  death-bed  can  never  recall  the  scene  without  horror ! 

Dipsomania  is  often  confounded  with  delirium  tremens ; 
but  though  it  rn^y  lead  to  that  disease  it  is  an  essentially 
*  Dr.  Greenfield,  in  "Alcohol :  its  Use  and  Abuse." 


33 6  ALCOHOL  AND  TOBACCO. 

different  pathological  state.  The  word  properly  means  a 
mental  disease  in  which  there  is  periodically  an  irresistible 
passion  for  alcohol ;  in  any  form,  no  matter  how  distasteful, 
the  dipsomaniac  will  swallow  it  with  avidity.  The  disease 
is  sometimes  produced  by  indulgence  in  drink,  but  is  more 
often  inherited,  especially  from  parents  addicted  to  alcoholic 
excess.  In  the  families  of  such,  one  child  is  often  epileptic, 
another  idiotic,  a  third  eccentric  or  perhaps  quite  mad,  and 
a  fourth  a  dipsomaniac.  When  the  fit  seizes  him  the  dipso- 
maniac is  as  irresponsible  as  a  raving  madman.  His  only 
safeguard  against  a  frightful  debauch  is  to  place  himself 
under  restraint  as  soon  as  he  perceives  the  symptoms  which 
he  has  learned  to  recognize  as  premonitory  of  his  fit  of  mad- 
ness. After  a  time  the  paroxysm  passes  off;  the  patient 
regains  self-control,  loses  his  passion  for  drink,  is  greatly 
ashamed  of  himself  if  he  has  indulged  it,  and  usually  behaves 
in  an  irreproachable  manner  for  some  weeks  or  months. 

The  sufferers  from  this  frightful  disease  are  entitled  to  a 
sympathy  to  which  the  common  drunkard  has  no  claim. 

III.  Chronic  and  often  Incurable  Diseased  Conditions 
produced  by  Alcohol. — These  are  apt  to  be  insidious  in  their 
approach,  and  overlooked  until  they  have  firmly  seated 
themselves.  They  include  (a)  deterioration  of  tissue;  (b) 
practical  destruction  of  important  organs;  (c)  mental  and 
moral  enfeeblement. 

(a)  Deterioration  of  Tissue  due  to  Alcohol. — A  serious 
structural  change  in  the  body  produced  by  alcoholic  excess 
is  fatty  degeneration.  The  oily  matter  of  the  body  exists  in 
two  forms :  first,  as  adipose  or  fatty  tissue  collected  under 
the  skin,  and  in  less  amount  elsewhere,  as  on  the  surface  of 
the  heart  and  around  the  kidneys;  second,  as  minute  fat- 
droplets  in  the  interior  of  various  cells  and  fibres.  Some 


DISEASED  CONDITIONS  PRODUCED  BY  ALCOHOL  337 

forms  of  alcoholic  drinks  tend  to  increase  the  adipose  tissue, 
and  may  lead  to  undue  accumulation  of  it  about  the  heart, 
impeding  the  action  of  that  organ.  A  more  important  and 
frequent  result  is  an  increase  of  fat-droplets  in  the  cells  of 
the  liver  and  the  muscular  fibres  of  the  heart,  the  oily  matter 
replacing  the  natural  working  substance.  A  heart  which  has 
undergone  this  change  is  commonly  spoken  of  by  patholo- 
gists  as  a  "  whiskey  heart  ";  for  although  fatty  degeneration 
of  the  heart  may  occur  from  other  causes,  alcoholic  indul- 
gence is  the  most  frequent  one.  Fatty  liver  or  fatty  heart  is 
rarely  if  ever  curable  ;  either  will  ultimately  cause  death.  It 
is  probable  that  in  both  cases  the  fatty  degeneration  is  due 
to  over -stimulation  of  the  organ.  Most  wines  and  spirits 
quicken  the  beat  of  the  heart,  leaving  it  less  time  for  repair 
between  its  strokes.  Alcohol  also  increases  the  breaking 
down  of  proteid  matter  in  the  body ;  the  liver  has  much  to 
do  in  preparing  this  broken-down  proteid  for  removal  by  the 
kidneys,  and  so  gets  overworked. 

Another  serious  bodily  deterioration  produced  by  alcohol 
is  fibrous  degeneration  :  by  this  is  meant  an  excessive  growth 
of  the  connective  tissue,  which,  as  we  have  seen  (p.  18),  per- 
vades the  organs  of  the  body  as  a  fine  supporting  skeleton  for 
the  more  essential  cells.  Alcohol -drinking  causes  this  tissue 
to  develop  to  such  an  extent  as  to  crush  and  destroy  the 
cells,  especially  in  the  liver  and  kidneys,  which  it  should 
protect.  So  far  as  the  liver  is  concerned,  the  result  is  a 
shrunken,  rough  mass  (hob-nailed  liver,  or  gin-drinker's  liver), 
with  hardly  any  liver  cells  left  in  it.  This  not  only  prevents 
the  proper  manufacture  of  bile  and  glycogen  (p.  130),  but 
the  contracted  liver  presses  on  the  branches  of  the  portal  vein 
within  it  (p.  177)  so  as  to  impede  the  drainage  of  blood  from 
the  organs  in  the  abdomen.  As  a  consequence,  an  excess  of 


33$  ALCOHOL  AND   TOBACCO. 

the  watery  part  of  the  blood  oozes  into  the  peritoneal  cavity 
and  accumulates,  causing  abdominal  dropsy  (asct/es^).  In  simi- 
lar manner  the  superabundant  connective  tissue  in  the  kid- 
neys crushes  and  injures  the  essential  kidney  substance,  and 
interferes  with  the  proper  function  of  the  organ  in  excreting 
nitrogen  waste  and  water.  The  ultimate  consequence  is  one 
form  of  "  Bright' s  disease  " — a  very  fatal  malady,  character- 
ized by  elimination  of  albumen  in  the  kidney  secretion  ; 
retention  of  proteid  wastes  in  the  blood,  poisoning  the  vari- 
ous organs ;  and  accumulation  of  water  in  the  loose  tissue 
binding  the  skin  to  underlying  parts,  producing  that  kind  of 
dropsy  known  as  anasarca. 

(V)  The  Organs  of  the  Body  most  apt  to  be  impaired  or 
destroyed  by  Alcohol  have  been  in  part  mentioned  in  pre- 
ceding pages.  It  will,  however,  be  convenient  to  collect 
them  together  and  point  out  the  kind  of  change  produced  in 
each.  Probably  no  tippler  ever  suffered  from  all  of  these 
diseases,  and  most  of  them  may  develop  in  persons  who  are 
total  abstainers  ;  but  the  organic  lesions  which  are  mentioned 
below  are  more  frequently  due  to  intemperance  than  to  any 
other  cause. 

A  primary  action  of  alcohol  after  absorption  is  to  cause 
dilatation  of  the  cutaneous  blood  vessels.  With  occasional 
alcoholic  indulgence  this  is  temporary ;  with  repeated,  it  be- 
comes permanent.  The  Skin  is  then  congested  and  puffy, 
and  on  exposed  parts  it  is  seen  to  have  a  purplish  or  reddish 
blotched  appearance ;  pimples  appear  on  parts,  such  as  the 
nose,  where  the  natural  circulation  is  more  feeble.  The  result 
is  the  peculiar  degraded  look  of  the  sot's  face.  The  conges- 
tion interferes  with  the  nutrition  of  the  skin  ;  the  epidermis 
(p.  200)  is  imperfectly  nourished  and  collects  in  scaly  masses, 


GKGANS  INJURED  BY  ALCOHOL  339 

interfering  with  the  proper  action  of  the  sweat  glands,  thus 
throwing  undue  work  on  the  kidneys. 

When  constantly  irritated  by  the  direct  action  of  strong 
alcoholic  drinks,  the  Stomach  gradually  undergoes  lasting 
changes.  Its  vessels  remain  dilated  and  congested,  its  con 
nective  tissue  becomes  excessive,  its  power  of  secreting  gas- 
tric juice  diminished,  and  its  mucous  secretion  abnormally 
abundant. 

The  Liver  suffers  fatty  and  fibrous  degeneration,  and  is 
one  of  the  organs  most  often  and  earliest  attacked.  This  we 
might  expect,  as  all  the  alcohol  absorbed  from  the  stomach  is 
carried  direct  to  the  liver  by  the  portal  vein  (p.  177). 

The  Heart  has  its  walls  at  first  thickened  (hypertrophied) 
and  its  cavities  dilated  by  the  excessive  work  (p.  337)  which 
alcoholic  drinks  stimulate  it  to  perform.  If,  as  is  usually  the 
case,  fatty  degeneration  ensues,  the  organ  gradually  becomes 
too  feeble  to  pump  the  blood  around  the  body,  and  death 
results. 

The  walls  of  the  Arteries  of  drinkers  frequently  undergo 
fatty  degeneration ;  they  lose  their  strength  and  elasticity, 
and  are  liable  to  rupture,  or  to  the  disease  known  as  aneu- 
rism . 

The  Kidneys  are  excited  to  undue  activity,  in  part  by  the 
dilatation  of  their  blood  vessels,  in  part,  perhaps,  through 
direct  stimulation  of  their  cells  by  alcohol  circulating  in  the 
blood.  Once  the  liver  is  attacked  the  nitrogenous  waste  of 
the  body  is  not  carried  to  the  kidneys  in  proper  form  foe 
excretion  :  some  is  held  back,  producing  a  tendency  to  gout 
and  rheumatism;  the  rest  is  got  rid  of  by  extra  kidney  effort. 
The  usual  result  is  fibrous  degeneration  of  the  kidneys,  caus- 
ing one  kind  of  Bright's  disease. 

The  Lungs,  from  the  congested  state  of  their  vessels  pro- 


340          ALCOHOL  AND  TOBACCO. 

duced  by  alcohol,  are  more  subject  to  the  influence  of  cold, 
the  result  being  frequent  attacks  of  bronchitis.  It  has  also 
been  recognized  of  late  years  that  there  is  a  peculiar  form  of 
consumption  of  the  lungs  which  is  very  rapidly  fatal,  and 
found  only  in  alcohol-drinkers. 

The  Sense  Organs  are  also  affected  ;  their  acuteness  of  per- 
ception is  dulled,  and  many  physicians  believe  that  cataract 
and  retinal  disease  may  be  produced  by  drinking.  The  red 
inflamed  white  of  the  eye  of  topers  is  well  known. 

The  Brain  and  Spinal  Cord  are  kept  in  a  chronic  state  of 
congestion*  and  over-excitement.  This  results  at  first  in 
inflammatory  disease  (delirium  tremens}  ;  later,  in  fibrous 
degeneration,  leading  to  certain  forms  of  paralysis  or  to  epi- 
lepsy, of  which  there  is  one  variety  well  recognized  by  phy- 
sicians as  due  to  alcohol. 

(c)  Moral  Deterioration  produced  by  Alcohol. — One 
result  of  a  single  dose  of  alcohol  is  that  the  control  of  the 
Will  over  the  actions  and  emotions  is  temporarily  enfeebled  ; 
the  slightly  tipsy  man  laughs  and  talks  loudly,  says  and 
does  rash  things,  is  enraged  or  delighted  without  due  cause. 
If  the  amount  of  alcohol  be  increased,  further  diminution 
of  will-power  is  indicated  by  loss  of  control  over  the  mus- 
cles. Excessive  habitual  use  of  alcohol  results  in  per- 
manent over-excitement  of  the  emotional  nature  and  en- 
feeblement  of  the  Will  ;  the  man's  highly  emotional  state 

*  "I  once  had  the  unusual  though  unhappy  opportunity  of  observing 
the  same  phenomenon  in  the  brain  structure  of  a  man  who,  in  a  fit  of 
alcoholic  excitement,  decapitated  himself  under  the  wheel  of  a  railway- 
carriage,  and  whose  brain  was  instantaneously  evolved  from  the  skull  by 
the  crash.  The  brain  itself,  entire,  was  before  me  within  three  minutes 
after  death.  It  exhaled  the  odor  of  spirit  most  distinctly,  and  its  mem- 
branes and  minute  structures  were  vascular  in  the  extreme.  It  looked 
as  if  it  had  been  recently  injected  with  vermillion." — Dr.  B.  W. 
Richardson. 


LOCAL  ACTION   OF  TOBACCO.  34 1 

exposes  him  to  special  temptation  to  excesses  of  all  kinds, 
and  his  weakened  Will  decreases  the  power  of  resist- 
ance :  the  final  outcome  is  a  degraded  moral  condition. 
He  who  was  prompt  in  the  performance  of  duty  begins 
to  shirk  that  which  is  irksome ;  energy  gives  place  to  indiffer- 
ence, truthfulness  to  lying,  integrity  to  dishonesty ;  for  even 
with  the  best  intentions  in  making  promises  or  pledges  there 
is  no  strength  of  Will  to  keep  them.  In  forfeiting  the  respect 
of  others  respect  for  self  is  lost  and  character  is  overthrown. 
Meanwhile  the  passion  for  drink  grows  absorbing  :  no  sacri- 
fice is  too  costly  which  secures  it.  Swift  and  swifter  is  now 
the  downward  progress.  A  mere  sot,  the  man  becomes 
regardless  of  every  duty,  and  even  incapacitated  for  any 
which  momentary  shame  may  make  him  desire  to  perform. 

For  such  a  one  there  is  but  one  hope — confinement  in  an 
asylum  where,  if  not  too  late,  the  diseased  craving  for  drink 
may  be  gradually  overcome,  the  prostrated  Will  regain  its 
ascendency,  and  the  man  at  last  gain  the  victory  over  the 
brute. 

Tobacco  contains  an  active  principle,  nicotin,  which  in  its 
pure  form  is  a  powerful  poison,  paralyzing  the  heart.  When 
tobacco  is  smoked  some  of  the  nicotin  is  burned,  but  there 
are  developed  certain  acrid  vapors  which  have  an  irritant 
action  on  the  mouth  and  throat.  The  effects  of  smoking  are 
thus  in  part  general,  due  to  absorbed  nicotin ;  and  in  part 
local,  due  to  irritant  matters  in  the  smoke.  They  vary  much 
with  the  constitution,  habits,  and  age  of  the  smoker.  One 
general  rule  at  least  may  be  laid  down :  tobacco  is  very  injuri- 
ous to  young  persons  whose  physical  development  is  not  com- 
pleted. 

The  Local  Action  of  Tobacco  is  at  first  manifested  by 
increased  flow  of  saliva.  This  usually  passes  off  after  some 


342  ALCOHOL  AND   TOBACCO. 

practice  in  smoking ;  dryness  of  the  mouth  follows,  and  con- 
sequent thirst,  often  leading  to  alcoholic  indulgence ;  and  in 
this,  perhaps,  lies  the  greatest  danger  from  tobacco.  The 
habitual  smoker  usually  suffers  eventually  from  what  is  known 
to  medical  men  as  "smoker's  sore-throat."  The  inflamma- 
tion often  extends  to  the  larynx,  injuring  the  voice  and  pro- 
ducing a  hacking  cough,  or  may  spread  up  the  Eustachian 
tubes  (p.  279)  and  impair  the  hearing.  Cigarettes  are  espe- 
cially apt  to  cause  these  symptoms.  Cure  is  impossible 
unless  smoking  be  given  up.  Those  who  draw  the  smoke 
into  their  lungs  often  suffer  from  chronic  inflammation  of  the 
bronchial  tubes  in  consequence. 

The  General  Action  of  Tobacco. — The  more  common 
effects  of  absorption  of  tobacco  products  are  to  interfere  with 
development  of  the  red  blood-corpuscles,  leading  to  pallor 
and  feebleness ;  to  impair  the  appetite  and  weaken  digestion ; 
to  affect  the  eyes,  rendering  the  retina  less  sensitive ;  to 
cause  palpitation  of  the  heart  and  enfeeblement  of  that 
organ ;  to  induce  a  lassitude  and  indisposition  to  exertion 
that,  in  view  of  the  heavy  odds  man  has  to  contend  with  in 
the  life-struggle,  may  prove  the  handicap  that  causes  his  fail- 
ure. If  success  in  life  be  an  aim  worth  striving  for,  it  is 
surely  unwise  to  shackle  one's  self  with  a  habit  which  cannot 
promote  and  may  seriously  jeopardize  it. 


APPENDIX  C 

DEMONSTRATIONS    AND    EXPERIMENTS.* 

BONES. 

Materials  :  Hind  leg  of  sheep  sawed  lengthwise  through  the 
joints.      Pieces  of  fresh  ivory  bone  (thin  bones 
such  as  are  found  in  the  legs  of  fowl,  will  an- 
swer).   Pieces  of  dry  ivory  bone. 
Reagents  :  Hydrochloric  acid  (HC1)  and  ammonia. 
Apparatus  :  Balance  with  metric  weights  from  i  centigram  to 
25  or  5°  grams.     The  balance  may  be  a  small 
hand  balance  carefully  adjusted. 
Human  skeleton  (such  as  may  be  purchased  for 

$25  or  $30). 
Microscope. 

Dissection  or  Demonstrations  : 

To  be  done  preferably  by  pupils  working  together  in  pairs  with  speci- 
men. 

i)   Structure  of  a  long  bone. 

<z)  Position  and  arrangement  of  dense  (ivory)  and 

cancellated  bone. 
£)  Medullary  canal. 

c)  Joint  ends  with  epiphyses. 

d)  Articular  cartilage. 

*  The  practical  work  is  planned  to  include  that  given  in  the  Outline  of 
Requirements  in  Anatomy,  Physiology  and  Hygiene  for  Admission  to 
Harvard  College  and  the  Lawrence  Scientific  School. 

343 


344  DEMONSTRATIONS  AND  EXPERIMENTS. 

e)  Periosteum. 

/)  Red  and  yellow  bone  marrow. 
g)  Microscopic  structure  of  bone. 
2  )  Composition  of  bone. 

0)   Boil  a  piece  of  fresh  bone  in  water  to   extract 
gelatin. 

b)  Burn  a  piece  of  fresh  bone  to  destroy  animal  matter. 

c)  Put  piece  of  fresh  bone  into  solution,  one  part 

hydrochloric  acid,  four  parts  water  (let  stand 
one  or  two  days  and  if  necessary  change  the 
solution)  to  remove  mineral  matter. 
Experiments  : 

i.   Proportions  of  water  and  solid  in  fresh  bone.      Break 
piece  in  small  fragments,  weigh,  dry  in  a  current  of 
warm  air  to  constant  weight  and  determine  loss. 
20.  Proportions  of  animal  and  mineral  matter  in  dry  bone. 
Weigh,  burn  on  a  piece  of  sheet  iron  over  live  coals 
or  on  a  piece  of  platinum  foil  over  Bunsen  burner  and 
weigh. 
2#.   Second  method.     Weigh,  dissolve  in  10$  hydrochloric 

acid,  dry  to  constant  weight  and  determine  loss. 
NOTE. — Demonstrate  the  presence  of  mineral  matter  in  the  solution  by 
precipitating  it  with  ammonia. 

JOINTS. 

Materials  :  Split  joint  of  sheep. 
Apparatus  :  Microscope. 
Dissection  or  Demonstrations  : 

a~)  Capsular  and  reinforcing  ligament. 

£)   Synovial  membrane. 

c)   Synovial  fluid. 

</)  Articular  cartilage. 

tf)   Functions  of  ligaments. 


MUSCLE.  345 

MUSCLE. 

Material  „•  A  frog. 

A  slice  of  meat  cut  across  the  grain  (a  low  cut  of 

the  leg  including  the  bone). 
Normal  salt  solution,  made  by  dissolving  y-J  gms. 

of  dried  table  salt  in  i  liter  of  water. 
Dissection  or  Demonstrations  : 

1)  Uncover  muscles  in  frog's  leg.     Note 

<z)   Outlines  of  muscles. 

£)   Tendon  attachments. 

c)  Relations  of  muscles  to  joints. 

2)  In  piece  of  beef,  note 

o)  Muscle  bundles. 

b)  Connective  tissue  boundaries  of  muscles  and  bun- 

dles. 

c)  Surface  or  intermuscular  tendon,  if  present. 

3)  Prepare  muscle  fibre  by  plunging  a  freshly  killed  frog 

into  water  at   55°  C.  (131°  F.)  and  allowing  it  to 
cool. 

a)  Tease  muscle  with  needles  in  normal  salt   solu- 

tion. 

b)  Examine  under  microscope. 

Experiment :  Proportions  of  water  and  solid  in  muscle.     (De- 
termine as  in  bone  (i). 

MUSCLE   ACTION. 

Materials  :   Calf  muscle    of  leg    of  frog  with   sciatic  nerve 
attached  (nerve-muscle  preparation). 

Apparatus  :  Induction  coil,  battery  and  wires.     A  small  coil 
such  as  is  used  by  physicians  will  answer  the 
purpose. 
Recording  apparatus  (Fig.  150). 


346 


DEMONSTRATIONS  AND  EXPERIMENTS. 


V)    D 

* 


II 


I 


i 


LEVERS.  347 

Experiments  (or  Demonstrations)  : 
What  results  follow 

<z)   Single  electrical  shock  through  nerve  ? 
£)   Single  electrical  shock  through  muscle  ? 
c)  Rapid  succession  of  shocks  through  nerve?     "Tet- 
anus. ' ' 
Demonstrations  : 

1)  Contraction  curve. 

2)  Curve  of  fatigue. 

a)  Regular  stimulation  at  intervals  of  one  second. 

b)  Tetanus. 
Directions  : 

For  the  contraction  curve,  the  smoked  glass  should  be 
moved  so  that  the  distance  between  the  rise  and  fall  of 
the  writing  point  will  be  one  or  two  inches. 

For  the  curve  of  fatigue,  the  smoked  glass  should  be  moved 
between  each  contraction  just  enough  to  allow  the  next 
contraction  to  make  its  own  record.  For  tetanus,  a 
slow,  continuous  movement  is  necessary.  The  rapid  in- 
terruption of  the  current  necessary  for  tetanus  can  easily 
be  accomplished  by  tapping  the  end  of  one  wire  on  a 
piece  of  tin  connected  with  the  other,  if  no  key  is 
available. 

LEVERS. 

The  leverage  conditions  in  the  body  may  best  be  studied 
by  means  of  an  apparatus  arranged  to  represent  the  action 
in  several  joints  (Fig.  151). 
Apparatus  :  Lever  apparatus. 
Problems  to  be  experimentally  solved  with  the  lever  apparatus. 

i)   Apparatus  arranged  to  represent  action  of  biceps. 

0)   How  much  force  must  the  biceps  exert  to  hold  a 


DEMONSTRATIONS  AND  EXPERIMENTS. 


i m 


FIG.  1st. — Lever  apparatus  for  studying  the  mechanics  of  muscles,  bones,  and 
joints — shown  as  arranged  for  the  study  of  forces  in  the  calf  muscles  and  ankle  joint. 
The  larger  figure  shows  two  connected  bars,  t  and  3  :  (i)  represents  either  the  bones 
of  leg  or  upper  arm,  and  (3)  those  of  the  foot  or  arm.  Another  view  of  the  joint 
is  shown  in  smaller  figure.  A  brass  sleeve  (2)  having  at  its  lower  end  the  joint  with 
the  brass  cross-arm  (3)  slips  easily  on  the  rod  (i)  and  forms  a  part  of  it.  The  joint 
pressure  is  measured  by  the  spring  scale  (4)  which  resists  the  pressure  of  arm  (3)  upon 
the  hinge  and  sleeve.  The  spring  scale  labelled  "  calf"  represents  the  calf  muscle, 
the  biceps  muscle,  or  the  triceps  muscle,  and  measures  the  force  each  is  made  to  exert 
according  as  iv  is  attached  as  represented  or  in  the  position  of  one  or  the  other  of  the 
dotted  lines.  The  pull  may  be  made  greater  or  less  by  moving  the  upper  attachment 
up  or  down  the  rod  (i).  The  spring  scalt  (c)  measures  the  effective  force  of  the  calf 
muscles  in  the  position  shown  and  may  be  changed  t\»  (#j  and  (Z1)  for  meas"ring  the 
effective  forces  of  the  biceps  and  triceps  muscles  of  the  arm  respecuvt  ~:y. 


LEVERS.  349 

pound  weight  in  the  hand  when  the  elbow  forms 
a  right  angle  and  the  forearm  is  horizontal  ? 
<$)  How  much  is  the  pressure  in  the  joint  under  the 
same  conditions  ? 

2)  Apparatus  arranged  to  represent  action  of  triceps. 

#)  How  much  force  must  the  triceps  exert  to  make 

the  hand  push  one  pound  ? 
b)  How  much  is  the  pressure  at  the  elbow  joint  ? 

3)  Apparatus  arranged  to  represent  action  of  muscles  of 

calf  of  leg. 

a)  When  a  person  of  150  Ibs.*  weight  is  stand- 
ing on  one  foot,  how  much  force  must  the 
calf  muscles  exert  to  raise  the  heel  from  the 
floor? 

£)  How  much  is  the  pressure  in  the  ankle  joint  ? 
Problems  to  be  solved  arithmetically.      Each  pupil  should  use 
his  own  weight  and  make  the  necessary  measurements  on 
himself  or  on  a  skeleton. 

1.  0)  How  much  force  do  the  calf  muscles  exert  in  rais- 

ing the  heel  from  the  floor  when  standing  on 
one  foot  ? 
b)  How  much  is  the  pressure  in  the  ankle  joint  ? 

2.  <z)   How  much  is  the  muscle  pull  through  the  patella 

to  raise  the  body  from  a  kneeling  posture  (the 

whole  weight  on  one  leg)  ? 

£)  How  much  is  the  pressure  in  the  knee  joint  ? 
3.  a)  How  much  does  the  biceps  pull  when,  by  flexing 

the  forearm,  50  Ibs.  are  raised  in  the  palm  of 

hand? 
b)  How  much  is  the  pressure  in  the  elbow  joint  ? 

*  Use  1.5  Ibs.  on  balance  to  represent  the  150  Ibs. 


35°  DEMONSTRATIONS  AND  EXPERIMENTS. 


OXIDATION. 

Materials  :  Magnesium  tape. 

Fine  emery  paper. 

Fine  iron  wire. 

Oxygen. 

Sulphur. 
Demonstrations  or  Experiments  : 

1 )  Rub  magnesium  tape  clean  with  emery  paper.     Cut  off 

two  pieces. 

a)  Apply  a  lighted  match  to  one  ;  note  manifesta- 
tions of  energy  and  changes  (magnesia)  in 
magnesium. 

£)  Place  the  other  in  a  bottle  with  a  few  drops 
of  water;  examine  in  a  day  or  so,  and  com- 
pare with  i)  a. 

2)  Attempt  to  burn  magnesia  obtained  from  i)  a. 

3)  Rub  the  iron  wire  bright  with  emery  paper. 

0)  Place  some  in  a  warm  dry  bottle  by  the  stove. 
£)  Place  some  in  a  bottle  containing  a  little  water, 

and  in  a  day  pr  so  compare  results  with  those 

from  3)  a. 

4)  Melt  a  drop  of  sulphur  on  end  of  iron  wire.     Ignite 

and  plunge  into  a  bottle  of  oxygen. 

# )   Note  manifestations  of  energy. 

£)  Note  changes  in  iron  and  compare  with  3)  b. 

FOODS. 

Materials :  Starch.     Dextrin.     Glucose.     Fat.     Sweet  Oil. 

Egg  albumin.      Cut  white  of  egg  repeatedly  with 
scissors,  shake  with  20  parts  water  and  filter. 


FOODS.  35  J 

Meat  juice,  i  Ib.  meat  finely  chopped,  soaked  for 
12  hours  in  four  parts  of  water  and  filtered. 

Peptone,  freshly  prepared  by  digesting  fibrin  or 
egg  albumin  in  an  artificial  gastric  juice. 

Reagents,  etc. :  Acetic  acid  (strong  vinegar).  Nit- 
ric acid.  Hydrochloric  acid.  Ammonia.  Sodic 
hydrate.  Sodic  carbonate.  Cupric  sulphate. 

Thick  starch  paste,  made  by  boiling  ordinary  corn 
starch. 

Acid  or  alkali  albumin,  made  by  heating  egg  albu- 
min with  5$  hydrochloric  acid  or  with  weak 
sodic  hydrate  solution. 

Milk. 

Tests  for  Food  Constituents* 

1)  Starch  and  dextrin,  dry  or  (better)  in  solution  with  a 

watery  solution  of  iodine — change  of  color.  This 
test  is  most  conveniently  made  with  drops  of  the  solu- 
tions on  a  white  plate. 

2)  Glucose,  maltose  or  lactose  solution  in  test  tube  with 

half  inch  strong  solution  caustic  soda  and  one  or  two 
drops  of  dilute  solution  sulphate  of  copper ;  shake  and 
boil — color  or  colored  precipitate.  (Trommer'  s  test. ) 

3)  Fat. 

#)   With  i  per  cent  solution  of  osmic  acid — color;  or 
b)   By  dissolving  in  ether  and  allowing  to  evaporate 
on  glass — grease  spot. 

4)  Egg  albumin  or  serum  albumin  in  dilute  solution. 

a)  Heat  in  test  tube — opacity  or  precipitate  ;  or 

b)  In  contact  with  strong  nitric  acid  poured  care- 

*  These  tests  cover  the  experimental  work  needed  as  a  preliminary  for 
digestive  experiments.  The  schedule  will  be  found  convenient  for  re- 
cording results. 


352 


DEMONSTRATIONS  AND  EXPERIMENTS. 


fully  and  slowly  down  side  of  test  tube — color 
or  precipitate. 

5)  Proteid. 

a)  Boil   with  strong  nitric  acid   (color) ;  cool  and 

make  alkaline  with  ammonia — color  or  colored 
precipitate  (Xanthoproteic  test),  or 

b]  With  strong  sodic  hydrate  solution  and  one  or 

two  drops  very  dilute  copper  sulphate — color 
(biuret  test). 

6)  Peptone.     Biuret  test— color. 

FOOD  MATERIALS. 


Tests. 

Starch. 

Dextrin. 

Glucose. 

Fat. 

Eg£- 
Albumin. 

Meat 
Juice. 

Peptone. 

Heat     

Iodine  

Xanthoproteic. 
Biuret 

Ether  

NOTE. — Students  may  be  tested  by  giving  them  mixtures  of  solutions 
or  other  food  substances  to  be  tested  for  fat,  sugar,  proteid,  starch,  etc. 
They  should  be  led  to  study  the  foodstuffs,  as  cabbage,  beets,  fruits,  etc., 
to  determine  their  constituents.  *  They  should  also  be  encouraged  to  find 
out  the  effects  of  cooking  and  to  report  to  the  class  results  of  experiments 
at  home.  The  water  in  which  food  substances  have  been  boiled  may 
also  be  studied. 

Demonstrations  : 

i)  Effect  on  thick  starch  paste  of 

a)  Saliva,  a  few  drops. 

b)  Pancreatic  extract,  a  few  drops  of  solution. 

*  Cellulose  is  not  easily  demonstrated  as  a  food  constituent.  It  may  be 
sometimes  shown  under  the  microscope  after  soaking  thin  sections  of  the 
substances  for  a  few  minutes  in  a  strong  watery  solution  of  iodine,  washing 
with  water,  transferring  to  dilute  sulphuric  acid  (2  parts  acid  to  i  part 
water  by  volume) ;  mount  the  sections  on  the  slide  in  acid  solution  and 
examine.  If  successful,  the  cellulose  is  left  blue. 


FOODS.  353 

2)  Effect  of  neutralizing  the  acid  or  alkali  albumin  by 

addition  of  weak  sodic  hydrate  solution  or  by  the 
addition  of  weak  acid  solution.  Color  with  litmus 
solution  in  order  to  determine  neutral  point. 

3)  Typical  emulsions  under  a  microscope  : 

a)  Milk. 

b]  Oil  which  has  been  shaken  with  solution  of  pan- 

creatic extract  of  bile. 
Experiments  :  Typical  foodstuffs. 

1)  Milk. 

a)  Determine  specific  gravity  with  hydrometer. 

b)  Determine  reaction  by  adding  a  few  drops  of  lit- 

mus solution. 

c)  i)   Warm  milk  in  small  beaker,  add  drop  by  drop 

a  dilute  solution  of  acetic  acid,  constantly 
stirring,  until  precipitation  (casein  and  fat); 
filter;  test  filtrate  by  Tro  miner's  test  (lac- 
tose). 

2)  Dry  residue  by  squeezing  it  in  the  fingers,  add 
to  a  small  portion  of  it  an  equal  amount  "of 
ether,  allow  it  to  stand  a  few  minutes,  put  a 
drop  of  the  ether  from  it  upon  a  watch  glass 
and  allow  to  evaporate  (fat)  ;  remove  ether 
from  the  residue  and  test  latter  by  the  Xan- 
thoproteic  test. 

2)  Flour.      Moisten  one  teaspoonful  of  flour  and  tie  the 

dough  in  a  piece  of  muslin.  Knead  thor- 
oughly, first  in  a  small  vessel  containing 
water,  saving  the  water,  and,  second,  in 
running  water  until  the  water  is  no  longer 
colored. 
a)  Determine  what  was  washed  out  of  dough. 


354  DEMONSTRATIONS  AND  EXPERIMENTS. 

b)  Examine  the  residue  (crude  glutin)   in  muslin  : 
observe  tenacity ;   determine  the  class  of  food 
materials  to  which  it  belongs. 
NOTE. — Other  food  stuffs  may  be  examined  with  profit. 


ANATOMY   OF   DIGESTIVE   TRACT. 

Materials:  Sound  and  diseased  natural  teeth  obtained  from  a 
dentist. 

Dilute  hydrochloric  acid. 

Rat  or  cat. 

Chloroform. 

An  inch  or  two  of  the  small  intestine  of  a  recently 
killed  calf. 

50$  solution  of  alcohol 

Normal  salt  solution. 

Hand  magnifier. 
Demonstration  : 

1)  After  having  soaked  the  sound  teeth  in  warm  water  for 

one  or  two  days  and  then  sawed  them  in  two  with  a 
fine  fret  or  scroll  saw,  examine  the  structure. 

2)  Demonstrate  the  excavations  of  teeth  by  decay. 

3)  Test  the  effect  of  an  acid,  as  dilute  hydrochloric  or 

vinegar,  upon  teeth. 
Di"cection  :  Kill  a  rat  or  cat  by  chloroform. 

i)  Dissect  away  the  skin  from  the  whole  ventral  aspect  of 
the  body  and  note  the  large  salivary  glands  in  the  neck 
region : 

a)  The  posterior  gland  (submaxillary),  rounded 
and  compact,  close  to  the  middle  line.  Raise 
the  submaxillary,  and  thereby  expose  its  duct, 
which  passes  forward  to  the  mouth,  into  which 


DIGESTIVE   TRACT.  355 

it  may  be  followed  by  separating  the  halves 
of  the  lower  jaw. 

b)  The    large    gland,   composed    of   several    loosely 

united  lobes  (parotid),  which  reaches  from 
the  neighborhood  of  the  ear  to  the  submaxil- 
lary.  Note  the  duct  of  the  parotid  which 
passes  forward  over  the  face  to  the  mouth, 
near  the  angle  of  which  it  passes  in  through 
the  cheek  muscles. 

c)  A  small  gland  in  front  of  the  submaxillary  (sub- 

lingual). 

2)  Remove    the    muscles,    etc.,   covering  the   larynx  and 

trachea ;  cut  away  the  front  and  side  walls  of  the 
chest  and  abdomen ;  remove  larynx,  trachea,  lungs, 
and  heart. 

a)  Note  the  gullet,  a  slender  muscular  tube  in  the 

neck,  and  trace  it  through  the  chest. 

b)  Sketch   the    relative  positions  of   the    abdominal 

viscera  before  displacing  any  of  them. 

3)  Turn  the  liver  out  of  the  way  and  follow  the  gullet  in 

the  abdomen  until  it  ends  in  the  stomach. 

a)  Note   the  form    of   the    stomach ;    its    projection 

(fundus)  to  the  left  of  the  entry  of  the  gullet; 
its  great  and  small  curvatures ;  its  narrower 
pyloric  portion  on  the  right,  from  which  the 
small  intestine  proceeds. 

b)  Notice  a  thin  membrane  (the  omentum)  attached 

to  the  stomach,   and  hanging  down   over  the 
other  abdominal  viscera. 

4)  Follow  and  unravel  the    coils    of  the    small    intestine, 

spreading  out  as  far  as  possible  the  delicate  membrane 


356  DEMONSTRATIONS  AND  EXPERIMENTS. 

(.iiecentery)  which  suspends  it  from  the  upper  dor- 
sal part  of  the  abdominal  cavity. 
a}  Note  blood   vessels  and    lacteals  running  in  the 
numerous  bands  of  fat  in  the  mesentery.      (The 
lacteals  are  best  seen  in  a  cat  killed  three  or 
four  hours  after  a  meal  of  rich  milk. ) 

5)  Open  into  the  side  of  the  large  intestine  opposite  junc- 

tion with  small. 

0)  Note  the  termination  of  the  small  intestine  (ileo- 
caecal  valve). 

b)  Observe    the    caecum  or  blind  end  of   the  large 

intestine,  projecting  on  one  side  of  the  point 
of  entry  of  the  small.  (Note  position  of  the 
vermiform  appendix  in  the  human  body.) 

c)  Follow   the  large    intestine    until  it   ends  at  the 

anal  aperture,   cutting   away    the  front  of  the 
pelvis  to  follow  its  terminal  portion  (rectum). 
</)   Note  the  colon,  the  portion  between  the  caecum 
and  the  rectum. 

6)  Spread  out  the  portion  of  the  mesentery  lying  in  the 

concavity  of  the  first  coil  (duodenum)  of  the  small 

intestine,  and  note 

a]  The  pancreas,  a  thin  branched  glandular  mass. 

£)  The  portal  vein  entering  the  under  side  of  the 
liver  by  several  branches. 

£)  Near  it  the  gall  duct,  formed  by  the  union  of  two 
branches  and  proceeding  as  a  slender  tube  to 
open  into  the  duodenum  about  an  inch  and  a  half 
from  the  pyloric  orifice  of  the  stomach. 

d)  The  spleen,  an  elongated  red  body  lying  behind 

and  to  the  left  of  the  stomach. 

e)  The  portal  veins ;  trace  them  to  the  liver. 


DIGESTION.  357 

7)  Divide  the  gullet  at  the  top  of  the  neck,  and  the  rectum 

close  to  the  anus,  and  severing  attachments,  remove 
the  whole  tube ;   then  cut  away  the  mesentery  and 
spread  it  out  at  full  length. 
#)   Note    the   relative    length    and   diameter    of    its 

various  parts    and    determine  the    ratio  of   its 

length  to  the  body  length. 

8)  Open  the  stomach  along  its  greater  curvature. 

#)  Note  the  thin  smooth  mucous  membrane  which 
lines  the  fundus,  and  is  sharply  marked  off  from 
the  thick  corrugated  mucous  membrane  lining 
the  rest  of  the  organ.  (This  is  not  the  case  in 
the  human  stomach.) 

£)  Examine  under  water  the  surface  of  the  lining 
membrane  with  a  hand  lens. 

9)  Remove  the  liver. 

#)   Note  its  general  form. 

<£)  Scrape  its  cut  surface  and  examine  cells  in  normal 
salt  solution  under  microscope. 

10)  Cut  out  piece  of  the  intestine  (or  that  of  calf),  wash 

inner  surface  gently  with  normal  salt  solution  and 
examine  in  solution  with  a  hand  lens.      Or 
n)   Place  a  piece  of  small  intestine  or  that  of  calf  in  50^ 
alcohol    for    twenty-four   hours.      Then    open   and 
examine  the  villi  under  water  with  a  hand  lens. 

DIGESTION. 

Materials:  Blood  fibrin.     This  can  be  obtained   by  stirring 
fresh  blood.      Dried  fibrin  may  be  used  for  diges- 
tion experiments,  or 
Egg  albumin,  coagulated.      Stir  white  of  egg  into 


35 8  DEMONSTRATIONS  AND  EXPERIMENTS. 

boiling  water  acidulated  with  vinegar  or  acetic 
acid. 

Meat  juice. 

Bile  of  pig  or  other  animal  obtained  from  butcher. 
Glycerole  pepsin.  Buy  of  druggist  or  collect  by 
taking  the  middle  portion  of  fresh  stomach  of 
pig,  scraping  off  the  mucous  membrane,  and 
adding  glycerin  to  it;  allow  to  stand  several 
days,  stirring  occasionally.  Use  a  few  drops 
for  each  experiment. 

Pancreatic  extract.  Purchase  of  druggist  or  pre- 
pare from  fresh  pancreas,  by  grinding  thoroughly 
with  sand  in  a  mortar,  a)  Add  water  to  one 
half  and  filter  through  cloth,  for  amylolytic  fer- 
ment, b)  Add  three  or  four  volumes  of  glycer- 
in to  the  remainder  and  allow  to  stand  several 
days,  for  proteolytic  ferment. 
Saliva.  Collect  by  chewing  paraffin  or  a  piece  of 

rubber,  and  filter. 

o.  2  per  cent  solution  of  hydrochloric  acid.  Add 
6.5  c.c.  commercial  hydrochloric  acid  to  i  liter 
of  distilled  water. 

Apparatus:  Water  bath  for  holding  test  tubes  in  digestion  ex- 
periments. An  oblong  deep  tin  pan,  contain- 
ing a  wire  test  tube  rack,  nearly  filled  with 
water  and  heated  by  a  Bunsen  burner,  lamp  or 
alcohol  lamp  will  answer.  Temperature  should 
be  kept  at  99°  F.  (38°  C). 
Thermometer.  Those  with  scales  on  stem  or  in 

glass  tubes  to  be  preferred. 

Test  tube  racks.     Wire  racks  with  a  capacity  for 
three  dozen  test  tubes  are  useful  in  water  bath. 


DIGESTION.  359 

Wooden  test   tube  racks  with  holes  and  pins 

should  be  supplied  to  the  tables. 
Dialyzer  (Fig.  66,  p.  145).     This  may  be  made 

from  a  section  of  a  lamp  chimney,   one  end 

being  covered  with  bladder,  intestine,  or  moist 

parchment  paper. 
Funnels.     For  students'  use,  they  should  be  two 

inches  in  diameter  j  for  preparing  material,  six 

or  eight  inches. 
Test  tubes.     A  dozen  six-inch  test  tubes  for  each 

student. 
Beakers.     Nests  of  three  beakers  of  from  four  to 

six  ounce  capacity. 
Filter  papers.     Three  inches   in   diameter   is   a 

convenient  size.     A  few  of  six  or  eight  inches 

diameter  will  be  needed. 

Litmus  rubbed  up  in  boiling  water  and  filtered. 
Demonstrations  : 

1)  Penetration  of  animal  membrane  (dialyzer)  by  crystal- 

loids (sugar,  salt)  and  peptone. 

2)  Non-penetration   of  animal   membrane  (dialyzer)   by 

colloids  (starch,  albumin)  except  peptone. 
Experiments  :   *  Use  a  test  tube  for  each  experiment.     Iden- 
tify them  by  slipping  bits  of  paper  con- 

*  The  digestion  ordinarily  requires  a  number  of  hours,  and  it  may  be 
best  to  prepare  the  solutions,  put  them  in  the  water  bath,  and  leave  them 
until  the  next  day  for  examination.  The  digestion  of  starch  and  of 
fibrin  if  shaken  every  few  minutes  is  so  rapid  that  it  may  be  possible  to 
get  the  proper  reactions  after  a  few  minutes  for  starch  and  after  half  an 
hour  for  fibrin.  If  the  laboratory  section  extends  for  two  hours,  as  it 
should  during  the  digestion  work,  the  digestions  may  be  sufficiently 
completed  at  the  end  of  that  time  for  all  the  characteristic  tests.  It  is 
best  under  these  circumstances  to  have  the  pupils  prepare  test  tubes 
first  then  have  the  demonstrations  and  experiments  which  can  be  accom- 


360  DEMONSTRATIONS  AND  EXPERIMENTS. 

taining  names  of  students  and  contents  in 
the  open  end.  Place  the  test  tubes  for 
all  digestion  experiments  in  that  portion 
of  the  water  bath  reserved  for  each  stu- 
dent. It  is  best  to  use  small  amounts  of 
substances  for  digestion,  and  fill  the  test 
tubes  about  two  thirds  full  of  solution. 
Two  or  three  drops  of  the  solution  of 
pepsin  and  of  pancreatic  extract  are  suffi- 
cient. Shake  frequently. 

1.  a)  Effect  of  saliva  on  starch  (38°  C.). 

b)  "  "  proteid  (38°  C.). 

c)  "  "  fat(38°C.). 

</)  Influence  of  temperature  (about  i8°C.  and  60°  C.). 

2.  a)  Effect  of  pepsin  on  boiled  fibrin  (38°  C.). 
3)       "          o.2f0  HC1     "          "          " 

c)      "          pepsin    and    0.2$    HC1   on    boiled   fibrin 

(38°  C.). 
</)  Influence  of  temperature  (about  i8°C.  and  60°  C.) 

on  action   of  pepsin   and   0.2$   HC1  on   boiled 

fibrin. 
e)  Test  product  of  gastric  digestion  (2,^)  for  peptones 

by  means  of  biuret  test. 

3.  a)  Effect  of  pancreatic  extract  on  starch. 

£)       "  "  "  fibrin  or  egg  albumin. 

plished  immediately,  to  be  followed  by  the  examination  of  digestion 
products  toward  the  end  of  the  exercise.  Students  sufficiently  inter- 
ested  and  with  plenty  of  time  to  do  quantitative  work,  may  deter- 
mine the  relative  rapidity  of  digestion  by  artificial  gastric  juice  and  by 
pancreatic  extract,  by  taking  weighed  amounts  of  fibrin,  exposing  them 
to  digestion  for  a  certain  length  of  time,  carefully  washing  and  reweigh- 
ing  the  fibrin  to  determine  the  amount  digested.  Experiments  may  also 
be  made  upon  the  time  taken  to  digest  raw  and  cooked  starchy  foods, 
etc.,  etc. 


STRUCTURE  AND  COMPOSITION  OF  BLOOD.       36* 

c)  Influence  of  acidity  and  alkalinity  on  action  of  pan- 
creatic extract. 

</)  Effect  of  shaking  oil  with  pancreatic  extract. 
0)       "       "  boiling  fat  or  oil  with  caustic  soda  or  caus- 
tic potash.      (Test  result  by  shaking  a  few  drops 
with  water. ) 
4.  Influence  of  bile  on  absorption  of  fats. 

a)  Moisten  a  filter  paper  stretched  across  top  of  a 
funnel  with  bile  and  put  on  paper  a  teaspoonful 
of  oil.  Moisten  another  filter  paper  similarly 
placed  with  water  and  apply  the  same  amount 
of  oil.  Note  comparative  rapidity  of  penetra- 
tion. 


STRUCTURE  AND  COMPOSITION  OF  BLOOD. 

Materials:  Frog. 
Ether. 
Blood  clot. 
Defibrinated  blood. 
Blood  serum. 
Apparatus:  Hand  magnifier. 

Microscope  with  powers  up  to  450. 
Bundle  of  twigs  or  wire. 
Two  fruit  jars. 
Demonstrations  : 

i)  Put  a  frog  in  a  solution  of  one  teaspoonful  of  ether  to  a 
quart  of  water,  and  cover  the  vessel  for  a  minute  or 
two.  Remove  the  frog,  cut  off  its  head  and  collect 
on  a  piece  of  glass  a  drop  of  the  blood  which  flows 
out.  Spread  out  the  drop  so  that  it  forms  a  thin 
layer  and  hold  the  glass  up  against  the  light. 


362  DEMONSTRATIONS  AND  EXPERIMENTS. 

a)  Examine  the  blood  with  a  hand  magnifier  and  a 
microscope,  noting  form,  size,  color,  and 
relative  numbers  of  red  and  white  corpuscles. 

2)  Wind  tightly  a  piece  of  twine  around  the  last  joint  of  a 

finger ;  then,  taking  a  needle,  prick  the  skin  of  the 
side  of  the  finger.  A  large  drop  of  blood  will  exude. 
Spread  it  out  on  a  piece  of  glass  under  a  cover  glass. 

a)  Examine  with  hand  magnifier. 

b]  Examine  with  microscope  and  demonstrate 

1)  Form,  size,  and  color  of  human  as  compared 

with  frog  red  blood  corpuscles. 

2)  Form  of  aggregation  of  human  blood  cor- 

puscles. 

3)  Color,  form,  size,  and  relative  number  of 

white  blood  corpuscles. 

3)  Obtain  a  large  drop  of  human  blood  as  above  (2)  de- 

scribed.    Note 

a)  Physical  characteristics  (color,  opacity,  etc. )  when 

it  flows  from  wound. 

b)  Apparent  change  of  color  when  it  is  spread  very 

thin  on  the  glass  and  held  over  a  sheet  of  white 
paper. 

c)  Color,  when  mixed  with  a  teaspoonful  or  more  of 

water  in  a  wine  glass. 

4)  Place  another  large  drop  of  human  blood,  obtained  as 

above,  on  a  clean  glass  plate.  To  prevent  drying  up 
cover  by  inverting  over  the  drop  a  wine  glass  whose 
interior  has  been  moistened  with  water. 

a)  In  four  or  five  minutes  remove  the  wine  glass  and 

note  the  condition  of  the  blood. 

b)  Replace  the  moist  wine  glass  and  in  half  an  hour 

examine  again. 


ANATOMY  OF  THE  HEART.  363 

5)  Collect  blood  at  butcher's  in  a  glass  jar ;  set  aside  until 

the  blood  clots  and  carry  it  home  with  the  least 
possible  shaking.  Observe  the  clot  and  serum  next 
day  ;  carefully  collect  latter. 

6)  Collect  blood  in  the  pail  and  beat  it  vigorously  with  the 

twigs  for  three  or  four  minutes. 

a)  Note  quantity  of  stringy  elastic  material  (fibrin) 

collected  on  the  twigs. 

b)  Wash  the  twigs  thoroughly  with  water  and  observe 

color  of  fibrin. 

7)  Take  some  of  the  serum  from  specimen  5. 

a)  Note  physical  characteristics. 

b)  Heat  it  in  a  test  tube. 

c)  Add  nitric  acid  to  some  in  test  tube. 

8)  Place  a  small  quantity  of  whipped  blood  (6)  on  a  piece 

of  platinum  foil.      Heat. 

a)  Note  that  after  the  drop  dries  it  blackens,  showing 

that  it  contains  much  organic  matter. 

b)  Continue    heating   until   this    is   burned    away ; 

examine  the  residue  of  white  ash,  consisting  of 
the  mineral  constituents  of  the  blood. 

ANATOMY  OF  THE   HEART. 

Materials:  Sheep's  heart,    not  cut  out  of  the  pericardium, 

severed  from  the  lungs,  nor  punctured. 
Dissection  *  or  Demonstration  : 

i)  Place  the  heart  and  lungs  on  their  dorsal  side  npon  a 
table  in  their  normal  relative  positions,  with  the  wind- 
pipe turned  away. 

*  The  dissection  may  be  made  before  the  meeting  of  the  class  and  the 
anatomical  facts  through  3)  c  demonstrated  upon  the  preparation. 


364  DEMONSTRATIONS  AND  EXPERIMENTS. 

a)  Note  the  pericardium  and  the  piece  of  diaphragm 

which  is  usually  found  attached  to  its  posterior 
end. 

b)  Inflate  lungs  and  note  relations  of  heart. 

2)  Carefully  dissect  away  adherent  fat,  etc. ,  without  cutting 

the  veins,  which,  being  thin,  collapse  when  empty 
and  may  be  easily  overlooked  until  injured.  As  each 
vein  is  found,  stuff  it  with  raw  cotton. 

a)  Note  the  vena  cava  inferior  on  the  under  (abdom- 

inal) side  of  the  diaphragm ;  thence  follow  it 
until  it  enters  the  pericardium. 

b)  Observe  the  hepatic  and  other  veins  which  the 

vena  cava  inferior  receives  from  the  liver,  spleen, 
kidneys,  and  diaphragm. 

c)  Observe  the  right  phrenic  nerve  lying  on  the  left 

side  of  the  inferior  vena  cava  and  ending  below 
in  several  branches  to  the  diaphragm. 

d)  Find  the  lower  end  of  the  superior  vena  cava, 

which  enters  the  pericardium  about  one  inch 
above  the  entry  of  the  inferior  cava;  thence 
trace  it  up  to  the  point  where  it  has  been  cut 
across. 

e)  Notice  between  the  ends  of  the  two  venae  cavae  the 

right  pulmonary  veins  proceeding  from  the  lung 
and  entering  the  pericardium. 

3)  Turn  the  right  lung  and  the  heart  back  to  their  natural 

position;    clear  away  the  loose  fat   in  front  of  the 
pericardium  ;  seek  and  clean  the  following  vessels  in 
the  mass  of  tissue  lying  anterior  to  the  heart  and  on 
the  ventral  side  of  the  windpipe.     Note 
.  •;-..:    i a)  The  aorta;  its  arch  and  branches. 

b)  The  pulmonary  artery  imbedded  in   fat  on  the 


ANATOMY  OF  THE  HEART.  365 

dorsal  side  of  the  aorta ;   note  course  and  follow 
branches  into  lungs. 

NOTE. — Observe   the  thickness   and  firmness  of  the 
arterial  walls  as  compared  with  those  of  the  veins. 

c)  The  left  pulmonary  veins  on  the  ventral  side  of 
the  left  pulmonary  artery,  passing  from  the  lung 
into  the  pericardium. 

4)  Slit  open  the  perieardial  sac,  and  note 

a)  Its  smooth,  moist,  glistening  inner  surface,  and 
the  similar  character  of  the  outer  surface  of  the 
heart. 

£)  The  character  and  amount  of  perieardial  fluid. 

5)  Cut   away  the  pericardium  carefully  from  the  various 

vessels  at  the  base,  and  note 

a)  While  this  is  being  done,  that  inside  the  pericar- 
dium the  pulmonary  artery  lies  on  the  ventral 
side  of  the  aorta. 

<5)   The  general  form  and  position  of  the  heart. 

6)  Carefully  dissect   out   the   entrance   of  the  pulmonary 

veins  into  the  heart.      It  will  probably  seem  as  if  the 
right  pulmonary  veins  and  the  inferior  cava  opened 
into  the   same  auricle,  but  it  will  be  found   subse- 
quently (13)  that  such  is  not  really  the  case.      Note 
on  the  exterior  the  following  points  : 
a)  The   flabby  auricle   (left)   into  which  the  veins 
open  and  its  companion  (right)  between  the 
aorta  and  the  superior  vena  cava. 
£)  A  band  of  fat  running  around  the  top  of  the  ven- 
tricles ;  an  offshoot  from  it  runs  obliquely  down 
the  front  of  the  heart,  passes  to  the  right  of  its 
apex  and  indicates  externally  the  position  of 
the  internal  partition  or  septum,  which  sepa- 


366  DEMONSTRATIONS  AND  EXPERIMENTS. 

rates  the  right  ventricle  (which  does  not  reach 
the  apex  of  the  heart)  from  the  left. 

7)  Dissect  away  carefully  the  collections  of  fat   around 

origins  of  the  great  arterial  trunks  and  around  the 
base  of  the  ventricles.     In  the  fat  will  be  found 
a)  A  coronary  artery  rising  from  the  aorta  close  to 
the  heart,  opposite  the  right  border  of  the  pul- 
monary artery  ;  it  gives  off  a  branch  which  runs 
in  the  groove  between  the  right  auricle  and 
ventricle,  then  runs  down  the  dorsal  side  of 
the  heart. 

£)  The  other  coronary  artery,   considerably  larger, 
rising  from  the  aorta  dorsal  to  the  pulmonary 
artery ;  its  main  branch  runs  along  the  ventral 
edge  of  the  ventricular  septum. 
e)  The  coronary  veins  accompanying  the  arteries. 

8)  Open  the  right  ventricle  by  passing  the  blade  of  a  scal- 

pel through  its  wall  about  one  inch  from  the  upper 
border  of  the  ventricle  and  on  the  right  of  a  band  of 
fat  which  marks  the  external  partition  between  the 
ventricle  (see  6,  b)  •  cut  down  towards  the  apex. 
Make  a  corresponding  cut  through  the  wall  of  the  same 
ventricle  on  its  other  side.  Raise  point  of  wedge- 
shaped  flap  and  expose  cavity.  Cut  off  the  pulmon- 
ary artery  about  an  inch  above  -its  origin  and  open 
the  right  auricle  by  cutting  a  piece  out  of  its  wall  at 
the  left  of  the  venae  cavse. 

a)  Pass  the  handle  of  a  scalpel  from  the  ventricle 
into  the  auricle,  and  also  from  the  ventricle 
into  the  pulmonary  artery ;  study  out  the  rela- 
tions of  these  openings. 
3)  Slit  open  the  auricle ;  note  the  fleshy  projections 


ANATOMY  OF  THE  HEART.  367 

(columns  carneae)  on  its  walls,  and  the 
smoothness  of  the  interior  surface  of  the  auri- 
cle. Observe  the  apertures  of  the  venae  cavae, 
and  note  that  the  pulmonary  veins  do  not  open 
into  this  auricle. 

c)  Behind  or  below  the  entrance  of  the  inferior  cava, 

note  the  entrance  of  the  coronary  sinus. 

d)  Pass  a  probe  through  the  aperture  along  the  sinus 

and  slit  it  open;  notice  the  muscular  layer 
covering  it  in. 

9)  Raise  by  its  apex  the  flap  cut  out  of  the  ventricular 

wall,  and  if  necessary  prolong  the  cuts  toward  the 
base  of  the  ventricle  until  the  divisions  of  the  tricus- 
pid  valve  come  into  view,  and  note 

a)  The  columnae  carneae  on  the  wall  of  the  ven- 

tricle, and  the  muscular  cord  (not  found  in  the 
human  heart)  stretching  across  its  cavity. 

b)  The  prolongation  of  the  ventricular  cavity  towards 

the  aperture  of  the  pulmonary  artery. 

10)  Cut  away  the  right  auricle. 

a)  Examine  carefully  the  triscupid  valve,  composed 
of  three  membranous  flexible  flaps,   thinning 
away    towards  their  free    edges ;    proceeding 
from    near  these  edges   are   strong  tendinous 
cords   (chordae  tendineae),  which  are  attached 
at  their  other  ends  to  muscular  elevations  (pap- 
illary muscles)  of  the  wall  of  the  ventricle, 
n)  Slit  up  the  right  ventricle  until  the  origin  of  the  pul- 
monary artery  comes  into  view.     Looking  carefully 
for  the  flaps  of  the  semilunar  valves,  prolong  the  cut 
between  two  of  them  so  as  to  open  the  bit  of  pulmon- 


368  DEMONSTRATIONS  AND  EXPERIMENTS. 

ary  artery  still  attached  to  the  heart.  Spread  out  the 
artery. 

a)  Examine  the  valves. 

b)  Observe  the  pouch  made  by  each  flap  and  the 

slightly  dilated  wall  of  the  artery  behind  it. 

c)  Note  that  the  free  edge  of  the  valve  is  turned  from 

the  heart,  and  has  in  its  middle  a  little  nodule 
(corpus  Arantii). 

12)  Open  the  left  ventricle  in  a  manner  similar  to  that 

employed  for  the  right.  Then  open  the  left  auricle 
by  cutting  a  bit  out  of  its  wall.  Cut  the  aorta  off 
about  half  an  inch  above  its  origin  from  the  heart, 
and  note 

a)  The  aperture  between  left  auricle  and  left  ventri- 

cle. 

b)  The  passage  from  the  ventricle  into  the  aorta. 

c)  The  entry  of  the  pulmonary  veins  into  the  auricle. 

d )  The  septum  between  the  auricles  and  that  between 

the  ventricles. 

13)  Pass  the  handle  of  a  scalpel  from  the  ventricle  into  the 

auricle ;  another  from  the  ventricle  into  the  aorta ; 
also  pass  probes  into  the  points  of  entrance  of  the 
pulmonary  veins. 

14)  Slit  open  the  left  auricle  and  note 

a)  The  columnae  carneae,  and  the  smoothness  of  the 

inner  wall. 

b)  The  columnse   carneae  of  the  ventricle,  also  the 

considerable  thickness  of  the  wall  as  compared 
with  that  of  the  right  ventricle  or  of  either  of 
the  auricles. 

15)  Carefully  raise  the  wedge-shaped  flap  of  the  left  ven- 

tricle, and  cut  toward  the  base  of  the  heart,   until 


HEART  ACTION.  369 

the  valve   (mitral)  between  auricle   and  ventricle  is 

brought  into  view. 

a)  Note  that  one  of  its  two  flaps  lies  between   the 

auriculo-ventricular  opening  and  the  origin  of 

the  aorta. 
ft)  Examine  in  these  flaps  their  texture,  the  chordae 

tendineae,  the  columnae  carneae,  etc. 
c)  Examine  the  semilunar  valves  at  the  exit  of  the 

aorta. 
1 6)  Slit  the  aorta  carefully  between  two  of  these  valves. 

a)  Examine  the  bit  of  aorta  still  left  attached  to  the 

heart  and  note  the  thickness  of  its  wall,  its 
extensibility  in  all  directions,  its  elasticity  and 
firmness. 

b)  Note  the  valves. 

c)  Note  the  origins  of  the  coronary  arteries  in  two 

of  the  three  dilatations  of  the  aortic  wall  above 
the  semilunar  flaps. 

d)  Compare  the  artery  with  the  veins  which  open 

into  the  heart. 

HEART  ACTION. 

Materials  :  Frogs.* 

Ether. 

Two  sheep's  hearts. 

Apparatus  :  A  piece  of  sheet  cork  or  of  thin  board  with  a 
half-inch  hole  cut  in  it. 

Microscope. 

Caliper  rule. 

*  Anatomically  a  frog's  heart  differs  in  many  respects  from  that  of  a 
mammal,  but  the  phenomena  of  systole  and  diastole  are  essentially  the 


37°  DEMONSTRATIONS  AND  EXPERIMENTS. 

Recording  apparatus,   similar  to   that    used    for 
muscle. 


FIG.  150. — Diagram  of  Marey  tambour  apparatus  for  recording  curves,  a,  the 
rubber  membrane  coinciding  with  the  movements  of  the  membrane  of  the  trans- 
mitting apparatus ;  6t  tambour  ;  c,  smoked  glass  plate. 


FIG.  151. — Diagram  of  cardiograph,    a,  cup;  6,  knob;  ct  spring;  </,  rubber  mem- 
brane. 

Cardiograph. 

Marey  tambour. 

Circulation  apparatus  made  from  bulb  syringe, 

such  as  may  be  obtained  at  the  drug  store. 
Manometer. 


HEART  ACTION. 


371 


V7 


FIG.  152.— Manometer. 


Several  feet  of  glass  tubing. 

Glass  nozzle  (glass  tubing  drawn  out  in  flame). 

Scalpel. 

A  piece  of  sheet  lead  such  as  comes  in  tea  chests. 

Scissors. 

Forceps. 

Rod,  Y  inch  diameter  (a  small  test  tube). 

Glass  window  (a  circular  piece  of  glass  i-J  inches 
in  diameter,  cemented  into  a  short  tin  tube). 

Graduate. 

Two  basins. 
Demonstrations  : 

i)  Take  a  medium-sized  frog.  Wrap  it  carefully  in  a  damp 
cloth  and  then  in  tea  lead  so  that  one  foot  is  outside 
the  lead.  Fasten  it  to  perforated  sheet  cork  or  board 


372  DEMONSTRATIONS  AND  EXPERIMENTS. 

and  pin  or  tie  toes  so  that  the  web  of  foot  is  spread 
over  hole.  Clamp  in  place  on  microscope  stage. 
Focus  carefully  on  web.  Note 

a)  Movement  of  blood  corpuscles. 

b)  Blood  vessels  in  which  blood  is  passing  toward 

finer  branches  (arteries) . 

c)  Smallest  vessels  through  which  blood  is  passing 

(capillaries). 

d)  Vessels   in    which   blood   is  passing  from  small 

branches  to  large  trunks  (veins). 

e)  Rapidity  of  movement  of  red  blood  corpuscles  and 

position  in  blood  stream      Also  bending  of  red 
blood  corpuscles  at  arterial  branches. 

f)  Movement  of  white  blood  corpuscles  and  their 

position  in  blood  stream. 

g)  Intermission   of  blood   flow  (?)  and  coincidence 
.    with  heart  beat. 

2)  Cut  the  medulla  oblongata  of  an  etherized  frog  by  nick- 
ing with  the  point  of  scalpel  at  right  angles  to  the 
length  of  the  body  in  the  line  joining  posterior  mar- 
gins of  the  ear  disks.  Introduce  a  blunt  wire  and 
destroy  the  brain  *  and  spinal  cord.  Run  a  pointed 
match  into  the  cut  to.  prevent  bleeding. 

Lay  the  animal  on  its  back,  and  carefully  divide 
with  scissors  the  skin  along  the  middle  line  of  the 
ventral  surface  for  its  whole  length.  Make  cross  cuts 
at  each  end  of  this  longitudinal  cut  and  pin  out  the 
flaps  of  skin. 

Next  pick  up  with  forceps  the  remaining  tissues  of 
the  ventral  wall  near  its  posterior  end,  and  divide 
them  longitudinally  a  little  on  the  left  side  of  the 
*  The  frog  is  in  this  way  painlessly  killed. 


HEART  ACTION.  373 

middle  line,  being  very  careful  not  to  injure  either 
the  viscera  in  the  cavity  beneath  or  a  large  vein  (an- 
terior abdominal)  running  along  the  wall  in  the  mid- 
dle line. 

About  the  point  where  the  vein  passes  from  the 
wall  to  enter  among  the  viscera  of  the  ventral  cavity 
are  the  bony  and  cartilaginous  tissues  of  the  sternal 
region.  Raise  the  posterior  cartilage  with  the  for- 
ceps, make  a  short  transverse  cut  in  front  of  the  vein, 
and,  looking  beneath  the  sternum,  note  the  pericar- 
dium with  the  heart  beating  inside.  Divide  the 
fibrous  bands  which  pass  from  the  pericardium  to  the 
sternum  and  with  scissors  cut  away  sternum,  etc., 
taking  great  care  not  to  injure  the  heart. 

Push  a  rod  of  about  half  an  inch  in  diameter  down 
the  throat  so  as  to  stretch  the  parts ;  then  picking  up 
the  pericardium  with  the  forceps,  open  it  and  gently 
cut  it  away. 
a)  Note  the  parts  of  heart : 

1)  Ventricle,  single  in  case  of  frog. 

2)  Auricles,  right  and  left. 

3)  Bulbus  arteriosus  on  front  aspect  of  heart. 

4)  Sinus  venosus  under  the  heart,  seen  by  gent- 

ly raising  the  apex. 

5)  Two  aortas. 

6)  Pulmonary  veins  and  vense  cavae. 

b)  Note  systole  and  diastole  of  heart. 

c)  Changes  of  color  and  size  of  its  parts. 

d)  Determine  the  order  of  contraction  of  the  dif- 

ferent parts. 
e)  Put  aside  under  a  bell-jar  with  a  wet  sponge,  or  a 


374  DEMONSTRATIONS  AND  EXPERIMENTS. 

piece  of  flannel  soaked  in  water.    Note  duration 

of  heart  beat. 

3)  To  demonstrate  the  action  of  the  valves  of  the  heart, 
carefully  remove  a  sheep's  heart  from  the  pericar- 
dium. 

a)  Aortic  valve. 

1)  Cut  off  aorta  one  inch  above  valves.     Tie 

into  it  a  piece  of  glass  tubing,  down  which 
pour  water.  Note  the  efficiency  of  the 
valves. 

2)  Tie  a  piece  of  glass  tubing  into  one  pulmonary 

vein  and  tie  off  the  other.  Fill  the  tubing 
with  water.  Squeeze  ventricles  with  hand 
and  note  results. 

b)  Mitral  valve. 

i)  Tie  into  the  left  auricle  a  glass  window  and 
watch  appearance  of  mitral  valve  as  ven- 
tricle is  squeezed  and  relaxed. 

c)  Mitral  and  tricuspid  valves. 

i)  Carefully  cut  the  auricles  away  from  another 
sheep's  heart,  taking  great  care  not  to  in- 
jure the  ventricles  or  the  auriculo-ven- 
tricular  valves.  Then  holding  the  ventri- 
cles, apex  down,  in  one  hand,  pour  water 
in  a  stream  into  them  from  a  pitcher  held 
about  a  foot  above.  Note  the  movement 
of  the  mitral  and  tricuspid  valves. 

4)  Take  bulb  syringe  and  fit  the  outflow  tube  to  receive 
either  a  piece  of  glass  tubing  about  two  feet  long  or 
apiece  of  pure  gum  rubber  tubing  (one  inch  "  sap  " 
tubing);  also  prepare  nozzle  with  a  hole  about  ^  inch 
in  diameter  which  can  be  fitted  to  the  distal  end  of 


HEART  ACTION.  375 

either  glass  or  rubber  tube.  A  basin  of  water  and 
another  basin  into  which  to  receive  the  discharge  are 
needed. 

a)  Put  aspirating  end  of  bulb  syringe  in  a  basin  of 
water ;  fill  syringe  ;  attach  glass  tube  ;  squeeze 
and  release  bulb  regularly  every  two  seconds. 
Note  character  of  outflow  and  measure  amount 
for  10  or  20  seconds.* 

V)  Attach  nozzle  to  end  of  glass  tube ;  pump  regu- 
larly as  before  and  note  character  of  outflow ; 
measure  outflow. 

c)  Remove  glass  tube  and  attach  rubber  tube.    Pump 
as   before,  noticing   character   of  outflow,  and 
measure  the  outflow  for  same  period. 
d  )  Attach  nozzle  to  rubber  tube  and  test  as  in  b) . 
e)   Determine  factors  contributing  to  uniform  flow. 
f)  Connect  a  manometer  with  the  arterial  side  of  the 
apparatus  and  measure  pressures  developed  in  a, 
b,  c,  and  d. 

g)  Determine  the  relation  of  the  internal  pressure  to 
the  size  of  the  rubber  tube  in  d  (the  flow  may 
be  conveniently  stopped  for  these  measure- 
ments). 

h)  Attach  a  large  tube  to  nozzle  (to  represent  vein) 
in  d  and  connect  another  manometer  to  it. 
Compare  pressures. 

5)  Record  human  pulse  curve  by' pressing  knob  of  cardio- 
graph (Fig.  151)  on  carotid  artery  at  side  of  larynx 
by  means  of  a  band  around  neck.  Connect  this 
with  a  Marey  tambour  (Fig.  150)  on  recording  appa- 

*  Attempt  should  be  made  to  squeeze  the  bulb  with  the  same  force 
throughout  these  experiments. 


376  DEMONSTRATIONS  AND  EXPERIMENTS. 

ratus  and  move  the  smoked  glass  *  over  the  writing 
point  to  separate  the  records. 

a)  Note  the  general  form  of  curve. 

b)  Note  the  dicrotic  wave. 

c)  Interpret  curve  in  relation  to  size  of  artery. 

ANATOMY  OF  THE  RESPIRATORY  TRACT. 

Materials:  Sheep's  lungs  with  windpipe  and  heart  attached, 
to  prevent  puncturing  of  lungs  through  careless 
removal  of  heart. 
Rat  or  kitten. 
Frog. 

Chloroform. 
Normal  salt  solution. 
Apparatus:  A  few  inches  of  glass  and  of  rubber  tubing  about 

i  inch  diameter. 

Some  small  object,  as  a  piece  of  cork  or  rubber. 
Microscope. 
Dissection  or  Demonstration: 

1)  Examine  the  windpipe  of  the  sheep  and  trace  its  division 

into  the  bronchi. 

a)  Notice  in  its  wall  the  horseshoe-shaped  cartilages, 
which  keep  it  open  and  which  are  so  arranged 
that  the  dorsal  aspect  of  the  tube  (which  lies 
against  the  gullet)  has  no  hard  parts  in  it. 

2)  Slip  a  rubber  tube  on  the  end  of  the  glass  tube  and  in- 

sert the  other  end  of  the  glass  tube  into  the  trachea ; 
tie  firmly;   blow  out  lungs  and  tie  rubber  tube  to 
keep  distended.     Note 
a]  The  extensibility  and  elasticity  of  the  lungs. 

*  The  record  may  be  "  fixed  "  by  flowing  the  plate  with  dilute  shellac 
varnish  and  letting  it  dry. 


ANATOMY  OF  THE  RESPIRATORY  TRACT.         377 

b)  The  size  and  form  the  lungs  assume  when  dis- 

tended. 

c)  The  space  for  the  heart. 

d)  The  concavity  of  the  lower  (diaphragm)  surface 

of  the  distended  lungs. 

e)  The  lobes. 

y)  The  pleural  membrane. 

3)  Trace  one  bronchus  to  its  lung. 

a)  Cut  through  the  lung  tissue  and  follow  the  branch- 

ing bronchi  through  the  lung. 

b)  Note  the  cartilage  rings  in  their  walls. 

c)  Note  mucous  membrane  lining  tubes. 

</)  Wash  surface  with  normal  salt  solution;  gently 
scrape  with  scalpel  and  examine  scrapings,  under 
microscope. 

4)  Remove  from  a  chloroformed  rat  or  kitten  the  abdominal 

viscera,   cutting   away  the   liver   and   stomach  with 
especial  care. 

a)  Examine  the  vaulted  diaphragm  and  through  it 
the  lungs. 

5)  Seize  some  of  the  folds  of  the  peritoneum  attached  to  the 

diaphragm  and  pull  it  down,  imitating  its  contraction 

and  flattening  in  inspiration. 

a)  Observe  corresponding  movements  of  lungs. 

6)  Make  a  free  opening  into  one  side  of  the  thorax. 

a)  Note  behavior  of  lung. 

7)  Open  the  other  side  of  the  chest. 

a)  Note  result  upon  the  lung. 

b)  Observe  the  structure  of  the  diaphragm  (its  ten- 

dinous centre  and  muscular  periphery)  and  also 
the  attachment  of  the  pericardium  to  its  thoracic 
side. 


37 8  MONSTRATIONS  AND  EXPERIMENTS. 

8)  Place  a  recently  killed  frog  on  its  back.     Fasten  lower 

jaw  wide  open. 

a)  Place  small  object  on  roof  of  mouth  near  nose. 

Note  movement. 

b)  Examine  scraping  from  roof  of  mouth  in  normal 

salt  solution  under  microscope. 

9)  Remove  as  much  of  oesophagus  as  possible ;    split  it 

open  and  pin  out. 

a)  Place  small  object  upon  it  near  mouth  end ;  note 

behavior. 

b)  Set   aside  under   moist  glass;     note   position    of 

mucus  on  surface  at  end  of  a  half-hour.* 


RESPIRATION. 

Materials:  Wood  shaving. 
Lime  water. 
Hydrochloric  acid. 

Blood  clot,  defibrinated  blood  or  piece  of  liver. 
Lungs  of  cat  or  rat. 
Apparatus:  Thermometer. 

Mirror. 

Wide -mouthed  bottle. 

Test  tube. 

Glass  tubes. 

Rubber  tubing. 

Bell-jar  of  two  quarts'  capacity. 

Sheet  rubber. 

Pinchcock. 

*  Cilia  are  present  in  the  respiratory  passages,  but  not  in  the  oesopt 
agus  of  man. 


RESPIRATION.  379 

Rubber  stopper  with  double  perforations,  to  fit 
bell -jar. 

Two  pieces  of  glass  tubing,  one  bent,  to  fit  per- 
forations of  stopper. 

Water- valve    respiration    apparatus    for    carbon 

dioxide. 
Experiments  and  Demonstrations: 

1 )  Note  the  effect  of  breathing 

a)  On  the  bulb  of  a  thermometer. 

b)  On  a  mirror,  knife  blade  or  other  polished  metalLc 

surface. 

2)  Burn  a  shaving  in  a  wide-mouthed  bottle  of  air  and 

close  tightly. 

a)  Pour  lime  water  into  the  bottle  and  shake.     Note 

result  (carbonate  of  lime). 

b)  Pour  a  few  drops  of  hydrochloric  acid  into  a)  and 

note  result. 

c)  Blow  breath  through  a  tube  into  a  solution  of  lime 

water. 

d)  Add  hydrochloric  acid  as  in  <5). 

e)  Demonstrate  by  means  of  the  water-valve  respira- 

tion apparatus  (Fig.  153)  the  relative  amounts  of 
carbon  dioxide  in  atmospheric  air  and  in  expired 
air,  by  partly  filling  bottles  with  lime  water  and 
breathing  through  them. 

3)  Blow  breath  through  a  weak  solution  of  lime  water 

colored  with  phenolphthalein.* 

4)  Cut  open  blood  clot  or  piece  of  liver. 

a)  Compare  freshly  cut  surface  with  surface  exposed 
to  air. 

*  Phenolphthalein  is  pink  in  alkaline  solutions,  colorless  in  acid. 


3  So 


DEMONSTRATIONS  AND  EXPERIMENTS. 


b)  Place  freshly  cut  piece  of  blood  clot  or  liver  into 

a  bottle  containing  oxygen.     Or 
>')   Shake    defibrinated    blood    in   bottle    containing 

oxygen.     Note  result  (oxyhaemoglobin). 


FIG.  153. — Apparatus  to  demonstrate  carbon  dioxide  in  expired  air.     «,  inspiration  ; 
expiration. 

5  Connect  manometer  by  a  piece  of  rubber  tubing  with  a 
piece  of  glass  tubing  in  the  mouth ;  place  also  in  the 
mouth  a  short  piece  of  tubing  J  to  •£  inch  diameter. 

a)  Breathe  as  ordinarily ;  note  changes  in  pressure  as 

shown  by  manometer. 

b)  Breathe  quickly  ;  note  changes  as  above. 

6)  Substitute    for  glass   tubing  in  5)  a  glass  tube  drawn 

out    to   a  point. 

a)  Breathe  as  ordinarily  ;  note  pressures. 

b)  Breathe  strongly  ;  note  pressures. 

7)  Connect  the  distant  end  of  the  rubber  tubing  from  the 

tube  in  the  mouth  to  the  Marey  tambour  and  record 
the  curves  made  by  the  writing  point. 


RESPIRATION.  3gl 

8)  Illustrate  the  action  of  the  diaphragm  by  substituting 
for  the  chest  wall  a  bell -jar  of  two  quarts'  capacity 
(Fig.  154).  Tie  the  lungs  of  a  cat  or  a  rat  on  a  long 
piece  of  glass  tubing  which  is  then  passed  up  from 


FIG.  154. — Breathing  apparatus,    a,  lungs  of  cat ;  3,  rubber  diaphragm  ;  c,  bowl ; 
,  pinchcock. 

beneath  through  one  of  the  perforations  in  the  stop- 
per. Seat  the  stopper  firmly  in  the  mouth  of  bell-jar. 
Stretch  a  piece  of  heavy  pure  gum  sheet  rubber  over 
the  larger  end  of  the  bell-jar  and  tie  it  firmly  in 
position.  Press  the  rubber  membrane  down  on  the 
top  of  a  bowl  and  close  the  rubber  tube  at  the  end  of 
the  bent  glass  tube  with  a  pinchcock. 

a)  To  represent  inspiration,  lift  the  bell-jar  from  the 

bowl,  allowing  the  rubber  membrane  to  flatten. 

b)  To  represent  expiration  press  the  membrane  on  the 

bowl. 

c)  To  represent  the  effect  of  a  puncture  of  .the  chest 

wall,  open  the  bent  tube,  when  the  jar  is  lifted 
from  the  bowl. 


3^2  DEMONSTRATIONS  AND  EXPERIMENTS. 

RENAL   ORGANS. 

Materials  : 

Rat. 

Chloroform. 
Fresh  sheep's  kidney. 
Apparatus  : 

Sponge. 
Bell  jar. 
Stout  scissors. 
Bristles. 
Dissection  or  Demonstrations  : 

Kill  a  rat  by  placing  it  under  a  bell-jar  with   a  sponge 
soaked  in  chloroform. 

1)  Open  the  abdomen,  remove  the  alimentary  canal, 

and  cut  away  with  stout  scissors  the  ventral 
portion  of  the  pelvic  girdle.  Note  the  dark  red 
kidneys  on  each  side  of  the  dorsal  part  of  the 
abdominal  cavity,  the  right  one  nearer  the  head 
than  the  left. 

2)  Dissect  away  the  connective  tissue,  etc.,  in  front 

of  the  vertebral  column,  so  as  to  clean  the  in- 
ferior vena  cava  and  the  abdominal  aorta. 

a)  Trace  out  the  renal  arteries  and  veins. 

b)  Find  the  ureter,  a  slender  tube   passing 

posteriorly  from  the  kidney,  and  trace 
it  to  the  bladder. 

3)  Dissect  away  the  tissues  around  the  urinary  blad- 

der.     Note  its  form,  etc. 

4)  Open  the  bladder. 

a)  Find  the   orifices    of  the  ureters,  and  pass 
bristles  through  them. 


ANATOMY  OF   THE  NERYOUS  SYSTEM.  383 

b)  Note  the  mucous  membrane  lining  the  blad- 
der. 

5)  Remove  one  kidney  from  the  body  and  divide  it 

from  its  outer  nearly  to  its  inner  border ;  turn 
the  two  halves  apart.  Examine  the  cut  surfaces 
and  note 

a)  At  the  inner  border  the  dilatation  of  the 

ureter. 

b)  The  outer  cortical  portion  of  the  kidney. 

c)  The  medullary  portion. 

d)  The  papillae. 

6)  Obtain  a  fresh  sheep's  kidney.     Divide  it  from  its 

outer  to  its  inner  border,  and  demonstrate 

a)  On  the  cut  surfaces  the  cortex  and  me- 

dulla. 

b)  The  pyramids   of  Malpighi  and  the  off- 

shoots of  the  cortex  extending  between 
them. 

ANATOMY  OF  THE  NERVOUS  SYSTEM. 

Materials  : 

Frog. 
Ether. 

Fresh  calf's  or  sheep's  head. 
Alcohol. 
Apparatus  : 

Stout  scissors. 
Bone  forceps. 
Dissection  or  Demonstrations: 

Kill  a  frog  with  ether ;   open  its  abdomen  and  remove 
the  viscera. 
a)  Note  at  the  back  of  the  abdominal  cavity  a  bundle 


384  DEMONSTRATIONS  AND  EXPERIMENTS. 

of  white  cords  (nerve  trunks)  passing  to  each 
leg. 

b)  Trace  the  sciatic  nerve  into  which  they  unite  and 
dissect  it  along  its  course  until  it  ends  in  fine 
branches  in  the  hind  leg. 

2)  With  stout  scissors  cut  very  carefully  bit  by  bit  the 

bodies  of  the  vertebrae  (which  will  be  seen  projecting 
in  the  middle  line  at  the  back  of  the  abdominal 
cavity)  until  the  neural  canal  is  laid  open  and  the 
spinal  cord  exposed.  Note 

a)  The  origin  of  the  nerves  from  the  spinal  cord. 

b)  Their  division  into  anterior  and  posterior  (ventral 

and  dorsal)  roots  before  they  join  the  cord. 

c)  The   ganglionic   enlargements    on   the    posterior 

roots. 

3)  Turn  the  frog  upon  its  abdomen  and  remove  the  skin 

and  muscles  on  the  dorsal  side  of  the  spinal  column. 
With  great  care  cut  away  the  upper  two  thirds  of  the 
neural  arches  of  the  vertebrae.  Then  remove  the 
upper  half  of  the  skull  cavity.  Gently  raise  the  brain 
and  spinal  cord,  divide  the  nerves  which  spring  from 
them  and  lift  out  the  whole  cerebro-spinal  system 
and  place  it  in  alcohol  for  twenty-four  hours.* 
Note 

a)  The  origin  of  nerves  from  both  brain  and  cord.f 

b)  The  union  of  the  brain  and  cord,  etc. 

4)  Dissect    away    the    skin    and    muscles    covering    the 

*  The  specimen  may  be  hardened  and  preserved  in  a  solution — forma- 
lin, 2  parts ;  alcohol,  20  parts ;  water,  78  parts. 

f  A  frog's  brain  differs  in  many  important  points  from  that  of  a  mam- 
mal, as  in  the  very  small  cerebellum,  the  comparatively  small  cerebral 
hemispheres,  the  comparatively  large  mid-brain  and  the  absence  of  con- 
volutions. 


ANATOMY  OF  THE  NERVOUS  SYSTEM.  385 

cranium  of  a  calf  s  or  sheep's  head.  Then  with  a 
small  saw  very  carefully  divide  the  bones  in  a  circular 
direction,  so  as  to  cut  off  the  crown  of  the  head.  Next 
carefully  remove  the  loosened  bones  of  the  top  of  the 
skull,  tearing  them  away  from  the  dura  mater  lining 
them. 

a)  Demonstrate  the  tough  dura  mater  enveloping  the 

brain. 

b)  Cut  it  away  and  note  the  processes  which  it  sends 

between  the  two  cerebral  hemispheres  and  be- 
tween the  cerebellum  and  the  cerebral  hemi- 
spheres. 

c)  Cut  the  membrane  away  and  note 

1)  Its    glistening    inner    surface,    due   to   the 

arachnoid  membrane  lining  it. 

2)  The   pia   mater   full   of  blood   vessels  and 

closely  attached  to  the  brain. 

3)  The  glistening  arachnoid  layer  covering  the 

exterior  of  the  pia  mater. 

d)  Put  the  specimen  aside  in  the  hardening  solution 

for  a  day  or  two.  When  the  brain  has  become 
somewhat  hardened  dissect  away  the  pia  mater 
on  one  side  and  show 

1)  The  cerebral  hemispheres  and  their  surface 

convolutions. 

2)  The  cerebellum  and  its  foldings. 

3)  The  medulla  oblongata  beneath  the  cerebel- 

lum. 

e)  With  bone  forceps  cut  away  the  remainder  of  the 

sides  and  roof  of  the  skull.     Find 

1)  Nerves  to  eyes. 

2)  Nerves  to  nose. 


DEMONSTRATIONS  AND  EXPERIMENTS. 

/)  Raise  the  brain  in  front  and  cut  through  the  ves- 
sels, nerves,  etc.  ,  which  attach  it  to  the  base  of 
the  skull  cavity  ;  remove  it  from  the  skull 
cavity. 

1)  The  cerebral  hemispheres,  which  overlap  the 

cerebellum  much  less  than  in  man. 

2)  Cerebellum. 

3)  Mid-brain,  etc. 

4)  Stumps  of  the  cranial  nerves  attached  to  the 

base  of  the  brain.* 

5)  Optic   commissure,   with   the    optic    tracts 

leading  to  it. 

6)  Stumps  of  the  optic  nerves  leading  from  it. 
g)  Make  sections  across  the  brain  in  different  direc- 

tions and  note 

1)  Gray  matter  spread  over  most  of  its  surface. 

2)  The  nodules  of  gray  matter  imbedded  in  its 

interior. 


NERVE  ACTION. 

Materials:  Frog. 

Blotting  paper. 
Vinegar. 

Apparatus:  Stout  scissors. 
Feather. 
Bone  forceps. 
Blunt  wire. 
Demonstrations  or  Experiments: 

i)   Feign  a  blow  at  a  person's  eye  after  having  told  him 
that  he  is  not  to  be  actually  struck. 

*  Most  of  these  will  have  been  torn  off  unless  the  dissector  has  some 
technical  skill. 


NERI/E  ACTION.  387 

2)  a)  Count  a  boy's  pulse  and  breathing  while  he  is  sitting 

quietly. 

b)  Let  him  run  a  hundred  yards  at  full  speed,  and 
immediately  count  pulse  and  breathing  movements. 
Compare  results. 

3)  Tickle  the  inside  of  the  nose  with  a  feather. 

4)  Place  a  live  frog  on  a  table  and  note  its  movements  and 

reactions  to  varying  conditions : 

a)  Breathing. 

b)  Winking. 

c)  Jumping,  etc. 
Voluntary  Reaction  (Chain  Reaction)  : 

5)  Divide  the  class  into  two  equal  groups  so  arranged  in 

series  that  a  signal  may  be  passed  from  one  to  another 
of  each  group  by  touching  hands.  Let  some  one  give  a 
signal  by  touching  the  hand  of  each  of  the  first  members 
of  the  two  series.  As  soon  as  the  pressure  is  felt,  let 
them  transmit  it  to  the  next  and  so  on  until  finally 
the  last  members  of  the  series  press  on  the  hands  of 
the  instructor,  who  decides  which  signal  came  first.* 

a)  Chain  reaction  with  eyes  shut. 

b)  Chain  reaction  by  one  series  with  eyes  shut,  other 

series  looking  on. 

c)  Conditions  in  b)  reversed. 
Reflex  Reaction  : 

6)  Prepare  a  frogf  by  destroying  its  brain  as  soon  as  it  is 

under  the  influence  of  ether. 


*  To  record  roughly  the  time  of  a  single  reaction  or  of  a  chain  reac- 
tion, the  inventive  teacher  can  use  a  pendulum  beating  seconds  and  a 
recording  apparatus  such  as  was  used  for  cardiograph  tracings,  with  a 
Marey  tambour  to  transmit  the  signal. 

\  This  is  best  done  an  hour  or  two  before  the  experiment. 


388  DEMONSTRATIONS  AND  EXPERIMENTS. 

a)  Note  reactions  of  frog 

1)  When  toe  is  pinched. 

2)  When  small  bits  of  blotting  paper  soaked  in 

vinegar  are  put  one  by  one  on  different  re- 
gions of  its  skin.  (Dip  the  animal  in  clean 
water  after  each  application  to  wash  away 
the  vinegar. ) 

b)  Destroy  its  spinal  cord  by  running  a  blunt  wire 

down  the  neural  canal.    Repeat  0  )  and  compare 
results. 

c)  Turn  frog  (<5)  on  its  back  and  carefully  expose  the 

origins  of  the  sciatic  nerves.     Pinch  these  and 
note  result. 

SPECIAL  SENSES. 

DERMAL   SENSES. 

Apparatus:  Drawing  compasses    (any  form,  not  too  sharp, 

may  be  used). 

Scale  graduated  to  millimeters. 
Vessel  of  cold  water. 
Vessel  of  lukewarm  water. 
Vessel  of  hot  water. 
Forceps. 
Experiments  (two  students  working  together) : 

i)  Take  a  straight  piece  of  hair  in  forceps  and,  by  ascer- 
taining the  greatest  length  which  will  give  rise  to  a 
sensation  of  pressure,  determine  the  relative  sensitive- 
ness of 

a)  Palm. 

b)  Back  of  hand. 

c)  Forehead. 


SPECIAL  SENSES.  389 

2)  What  is  the  least  distance  that  the  two  points  of  the 

compasses  may  be  separated  and  still  be  recognized 
as  two  when  applied  to 

a)  Finger  tip  ? 

b)  Back  of  hand  ? 

c)  Back  of  neck  ? 

3)  a)  What  sensations  are  caused  by  the  light  pressure  of 

a  pencil  point  on  the  back  of  the  hand  ? 
&)  Are  the  cold  points  constant  in  their  position  ?    (Test 
from  day  to  day. ) 

4)  Temperature  sense. 

a)  Put  a  finger  of  the  right  hand  into  warm  water  and 

a  finger  of  the  left  hand  into  cold  water.  Note 
the  immediate  sensations  and  the  change  in 
sensations  after  the  fingers  have  remained  some 
time  in  the  water. 

b)  Withdraw  the  fingers  and  plunge  both  immediately 

into  the  vessel  containing  lukewarm  water. 
Compare  the  sensations  of  the  two  fingers. 

TASTE   AND    SMELL.* 

Materials  :  Onion.  Dilute  ammonia  (one  drop  of 

Sugar.  strong  ammonia  in  a  glass 

Salt.  of  water). 

Dilute  Vinegar.       Cabbage. 

Carrot.  Quinine. 

Experiments  (two  students  working  together)  : 

i)  Eliminate  odor  by  holding  the  nose  and  determine 

*  Care  should  be  taken  not  to  exhaust  the  sense  organs  by  over-stim- 
ulation. 


39°  DEMONSTRATIONS  AND  EXPERIMENTS. 

a)  Which  of  these  materials  have  odor. 

b~)  Which  have  taste.     Classify  them. 

c)  Where  ' '  taste  ' '  is  located  in  the  mouth. 

HEARING. 

Apparatus  :  Tuning  fork  and  resonance  chamber. 

Stretched  wire  or  catgut  (violin). 

Violin  bow. 
Demonstrations  and  experiments  : 

1.  Sound  dependent  on  vibration. 

2.  Pitch*         "  "  rapidity  of  vibration. 

3.  Volume       "  "  extent  of  vibration. 

4.  "  "  "  resonance. 

5.  Test  of  acuteness  of  hearing  with  watch  at  varying  dis- 

tances from  ear. 

6.  Test  the  sense  of  direction  by  hearing, 

a)  Using  both  ears  and  closing  eyes. 

b)  Using  one  ear       "        "          "  . 

VISION. 

Materials  :  Fresh  eye  of  white  rabbit,  calf  or  sheep. 
Apparatus  :  Cards  with  two  parallel  fine  black  lines  -^  m.m. 

apart. 

Cards  for  blind  spot  (spots  2  in.  apart). 
Worsteds  for  color  test  (Milton  Bradley).     One 
skein  of  each  of  the  standard  prismatic  colors 
with  their  tints  and  shades  will  supply  a  large 
class  if  cut  up  into  small  hanks. 

*  Pitch  may  be  graphically  demonstrated  by  means  of  a  manometric 
flame  and  a  revolving  mirror,  using  the  voice  or  a  cornet  for  the  produc- 
tion of  tones. 


VISION.  39 x 

Color  top  with  color  disks  (Milton  Bradley). 
Prism.      A  small  glass  prism,  60°  angles. 
Photographic  camera.    Any  photographic  camera 

which  has  a  ground  glass  will  answer. 
Spectacle  lenses,  concave  and  convex. 
Candle. 
Screen,  a  piece  of  cardboard  placed  in  a  vertical 

position  on  base. 
Demonstrations  : 

1)  Remove  eye  from  the  socket  of  a  freshly  killed  rabbit. 

Point  eye  toward  a  window  and  note 

a)  Image  of  window  on  retina. 

b)  Size  and  inversion  of  image. 

2)  Demonstrate   formation    of  image  by  a  lens.     Use  a 

camera  with  ground  glass,  or  an  ordinary  magnifying 
glass,  and  receive  image  on  paper. 

3     Demonstrate   effect   of  diaphragms  on  brightness  and 
sharpness  of  image. 

4)  Analyze  white  light  by  means   of  a  prism,    throwing 

spectrum  on  white  paper. 

5)  Mix  colors  by  means  of  color  top. 

a)  Black  with  white  in  different  proportions  (grays). 
3)  Various  colors  with  white  (tints). 

c)  "          "        «     black  (shades). 

d)  "          "        "     each  other. 

6)  Test  color  blindness  by  giving  to   pupil  a  set  of  the 

standard  colors  and  their  tints  and  shades  ;  hold  up 
color  and  ask  for  the  selection  of  all  pieces  resem- 
bling it. 

7)  Use   lenses   and  lighted  candle  for  the  formation    of 

actual  images. 


392  DEMONSTRATIONS  AND  EXPERIMENTS. 

a)  Near   sightedness.      Arrange   screen  just   behind 

the  focus  of  lens  (image  on  screen  somewhat 
blurred).  Place  concave  spectacle  lens  in  front 
of  magnifying  glass  and  note  result. 

b)  Far  sightedness.     Arrange  screen  just  in  front  of 

the  focus  of  lens   (image   on  screen  somewhat 
blurred).    Place  convex  spectacle  lens  in  front 
of  magnifying  glass  and  note  result. 
8)   Indicate  by  means  of  diagrams 

a)-  Corresponding  parts  of  retinae. 
b)  How  size  and  distance  of  objects  are  estimated. 
Experiments  : 

1)  Sharpness  of  vision. 

What  is  the  farthest  distance  at  which  the  two  parallel 
lines  on  card  can  be  seen  as  two  (using  one  eye) 

a)  When  card  is  held  in  line  of  vision  ? 

b)  When  card  is  held  20°  away  from  line  of  vision  ? 

2)  Changes  in  iris. 

a)  Sit  facing  a  window ;  cover  one  eye  with  hand  for 

one  minute.  Quickly  uncover  eye  and  note 
changes  in  pupil  by  means  of  a  mirror. 

b)  Observe  eye  of  companion  in  a  uniformly  lighted 

room  or  out  of  doors,  and  compare  the  size  of 
pupil  when  looking  at  a  distant  object  with  that- 
when  looking  at  an  object  six  inches  away. 

3)  Blind  spot. 

What  is  the  distance  at  which  the  right  hand  spot  on 
card  disappears  when  one  looks  at  the  left  spot  with 
right  eye,  holding  the  card  so  that  the  spots  are 
on  the  same  level  ? 

(Draw  a  diagram  of  an  eye  and  locate  the  axis  of 
vision,  blind  spot,  lens,  iris,  cornea,  retina.) 


VISION.  393 

4)  Accommodation :  Determine  the  range  of  accommoda- 

tion in  your  own  eye. 

5)  Binocular  vision. 

a)  Hold  two  pencils  vertically  in  front  of  the  eyes, 

one  at  a  distance  of  one  foot,  the  other  at  two 
feet.  When  looking  at  either  one  what  is  the 
appearance  of  the  other,  and  why  ?  Show  by 
diagram. 

b)  Under  what  conditions  do  you  see  "  single ' '  when 

using  both  eyes  ? 

6)  What   are  the  movements  of  the  eyeballs  in  changing 

from  far  to  near  vision  ? 

7)  Test  visual  judgment  of 

a)  The  sizes  of  disks  of  different  colors  (black,  white, 

red,  etc. )  but  of  the  same  size. 

b)  The  lengths  of  vertical  and  horizontal  lines  of  the 

same  length. 

c)  The  two  halves  of  a  line,  one  of  which  is  crossed 

by  several  short  lines. 


INDEX. 


ABDOMINAL  aorta,  170 

Abdominal  cavity,  8,  10 

Abdominal  respiration,  206 

Abduction,  49 

Absorbents,  85,  159,  161  ;  rela- 
tion of,  to  excretion,  86 

Absorption,  from  the  mouth, 
pharynx  and  gullet,  144  ; 
from  the  stomach,  144  ;  from 
the  small  intestine,  144;  from 
the  large  intestine,  146 ;  of 
fats,  139 

Accommodation,  276 

Acetabulum,  47 

Acid,  acetic,  97;  glycocholic, 
139;  hydrochloric,  15,  135; 
oleic,  18;  palmitic,  i6;stearic, 
16;  taurocholic,  139 

Acinous  glands,  107,  109 

Adam's  apple,  290 

Afferent  (sensory)  nerves,  250, 
252 

Air,  changes  produced  in,  by 
being  breathed,  209;  neces- 
sary quantity  of,  for  each  per- 
son,212;  quantity  of,  breathed 
daily,  199,  208;  renewal  of,  in 
the  lungs,  204;  unwholesome, 
212;  why  the  lungs  fill  with, 
204. 

Air-passages,  195;  cilia  of,  195 

Air-sacs,  197 

Albumin,  egg,  15,  93;  serum, 
15 

Albuminous  (proteid)  sub- 
stances, 15;  action  of  bile  on, 
139;  of  gastric  juice  on,  135; 
of  pancreatic  secretion  on, 
137;  special  importance  of,  as 
food,  89 


Alcohol,  98;  as  a  food,  98 

Alimentary  canal,  6,  84;  ab- 
sorption from,  143;  anatomy 
of,  no;  general  arrangement 
of,  106;  subdivisions  of,  no 

Alimentary  principles,  93;  car- 
bohydrate, 94;  hydrocarbon, 
94;  inorganic,  95;  proteid,  93 

Alveoli  (see  Air-sacs) 

Amoeba,  151 

Amyloids  (see  Carbohydrates) 

Amylopsin,  131 

Anaemia,  157 

Anatomy,  human,  I,  2,  12 

Anatomy,  microscopic  (see 
Histology) 

Anatomy,  of  alimentary  canal, 
no;  of  circulatory  organs, 
163;  of  ear,  279;  of  eyeball, 
269;  of  joints,  46;  of  larynx, 
289;  of  liver,  128;  of  muscular 
system,  52;  of  nervous  sys- 
tem, 230;  of  respiratory  or- 
gans, 193;  of  skeleton,  17;  of 
skin,  222;  of  urinary  organs, 
251 

Animals,  classification  of,  6 
(foot-note) 

Animal  charcoal,  43 

Animal  heat,  76 

Ankle  joint,  33,  49 

Antitoxin,  302 

Anvil  (incus)  bone,  280 

Aorta,  163,  166;  thoracic,  170; 
abdominal,  170 

Apex  beat  (cardiac  impulse), 
1 80 

Apex  of  heart,  165 

Appendicular  skeleton,  20 

Appetite,  cause  of,  142 

395 


396 


INDEX. 


Aqueous  humor,  273 

Arachnoid,  235 

Arch  of  foot,  32,  35 

Areolar  tissue,  subcutaneous, 
222 

Arm,  skeleton  of,  21 

Arterial  blood,  150,  179 

Arterial  pressure,  189 

Arteries,  164,  169  ;  aorta,  166  ; 
axillary,  170  ;  brachial,  170  ; 
cceliac  axis,  170 ;  common 
iliacs,  170;  coronary,  168,  169; 
femoral,  170  ;  hepatic,  128  ; 
innominate,  169  ;  left  com- 
mon carotid,  169 ;  left  sub- 
clavian,  169;  mesenteric,  170; 
peroneal,  170;  popliteal,  170; 
pulmonary,  167  ;  radial,  170, 
186;  renal,  170,  215,  218;  right 
common  carotid,  170 ;  right 
subclavian,  170;  temporal, 
186  ;  tibial,  170  ;  ulnar,  170  ; 
vertebral,  170 

Arteries,  course  of  the  main, 
169;  muscles  of  the,  190; 
properties  of  the,  170 ;  why 
placed  deep, 173 

Arterioles,  172 

Articular  cartilage,  20,  38 

Articular  extremities  of  bones, 

38 
Articulations,  19 

Arytenoid  cartilages,  291 
Assimilation,  85,  86 
Astigmatism,  276 
Astragalus,  32    • 
Atlanto-axial  articulation,  24 
Atlas  vertebra,  24 
Auditory  nerve,  242 
Auricles,  166  ;  function  of  the, 

183 

Auricular  contraction,  181 
Auriculo-ventricular  orifice,  166 
Auriculo  -  ventricular     valves, 

169,  181 

Auscultation,  204 
Automatic  nerve  centres,  255 
Axial  skeleton,  20 
Axillary  artery,  170 
Axis      cylinder      (neuron)      of 

nerves,  245 
Axis  vertebra,  24 


BACKBONE  (see  Vertebral  col- 
umn) 

Bacteria,  301 

Ball  and  socket  joint  (enarthro- 
sis),  48 

Basement  membrane,  109 

Base  of  heart,  165 

Bathing,  192,  228  ;  proper  time 
for,  229 

Baths,  shower,  229  ;  warm, 
229 

Beans,  nutritive  value  of,  98 

Beef-tea,  61 

Biceps  muscles,  definition  of, 
52,  55  56 

Bicuspids  (premolars),  112 

Bile,  129,  139  ;  action  of,  in  fat 
absorption,  139  ;  uses  of,  139 

Bile  duct,  common  (ductus  com- 
munis  choledochus),  129 

Bi-penniform  muscles,  56 

Bladder,  urinary,  215 

Blind  spot,  272 

Blister,  220 

Blood,  arterial  and  venous,  150, 
179  ;  changes  undergone  by, 
in  the  lungs,  214  ;  circulation 
of,  176  ;  coagulation  of,  152  ; 
colorless  corpuscles  of,  150  ; 
flow  of,  in  the  capillaries  and 
veins,  187-;  functions  of,  147, 
148  ;  gases  of,  155  ;  histology 
of,  148  ;  as  a  medium  of  ex- 
change, 155;  hygiene  of,  156; 
quantity  of,  in  the  body, 
157  ;  red  corpuscles  of,  149; 
whipped  (defibrinated),  153 

Blood-plasma,  148,  152 

Blood-serum,  152  ;  composition 
of,  154 

Blushing,  190 

Body,  centre  of  gravity  of,  68; 
chemical  composition  of,  14; 
constructive  power  of,  89  ; 
co-operation  of  the  organs  of, 
230  J  daily  need  of  foods  by, 
100;  general  plan  of,4;  levers 
in  the,  64;  movements  of,  46; 
oxidations  in,  78  ;  oxygen 
food  of,  81  ;  pulleys  in,  67  ; 
quantity  of  blood  in,  157 ; 
resistance  of  body  to  infec- 


INDEX. 


397 


tion,  151 ;  temperature  of,  77; 
wastes  of,  83. 

Bones,  chemical  composition 
of,  42;  fractures  of,  44  ;  func- 
tion of,  17  ;  gross  structure 
of,  36  ;  histology  of,  40  ;  in- 
ternal structure  of,  38  ;  of 
cranium,  28  ;  of  ear,  329  ;  of 
face,  29  ;  of  lower  limb,  21  ; 
of  pectoral  arch,  20;  of  pelvic 
arch,  21  ;  of  upper  limb,  21  ; 
reason  that  they  are  hollow, 
38;  varieties  of,  39 

Bone-ash,  43 

Bone-black    (animal   charcoal), 

43 

Bone  corpuscles,  42 
Bony  skeleton,  20;  hygiene  of, 

43 

Brachial  artery,  170 
Brain,  234,  283;  growth  of,  261; 

hygiene  of,  261;  localization, 

257 

Bread,  composition  of,  92; 
wheaten,  superiority  of, 97 

Breastbone,  20,  28 

Bronchi,  195 

Bronchitis,  196 

Buccal  cavity  (see  Mouth  cav- 
ity) 

Butter,  94 

Butyrin,  94 

CABBAGE,  nutritive  value  of, 
98 

Caecum,  126 

Calcaneum  (heel  bone),  32 

Calcium  carbonate,  15,  43 

Calcium  phosphate,  15,  43,  44, 
96 

Calices  of  kidney,  217 

Canaliculi  of  bone,  41 

Cane  sugar,  95 

Canine  teeth,  112 

Capillaries,  164,  172;  absence  of 
pulse  in,  189;  circulation  in, 
187.  188;  pulmonary,  169;  sys- 
temic, 166 

Capsular  ligament,  47 

Carbohydrates  (amyloids),  16, 
94;  kinds  of,  in  the  body,  16 

Carbonate  of  lime,  15,  43 


Carbon  dioxide,  as  a  waste 
product,  83;  in  the  blood,  155; 
percentage  of,  in  unwhole- 
some air,  211,  213;  quantity 
of,  passed  from  the  lungs  in 
a  day,  210;  useless  as  a  food, 
90 
Cardiac  impulse  (apex  beat), 

1 80 

Cardiac  orifice  of  stomach,  121 
Cardiac    period,  events   occur- 
ring in  a,  181 
Cardio-motor  nerves,  252 
Carotid  arteries,  169,  170 
Carpal  bones,  21,  39;  joints  be- 
tween, 51 

Carrots,  nutritive  value  of,  98 
Cartilage,  articular,  20,  38;  cells 
of,  17;  costal,  28;  function  of, 
25;  intervertebral,  22,  25 
Casein,  16,  93;    vegetable,  93 
Cells,  ii,  12;  air,  of  lungs,  197; 
cartilage,  17;   ciliated,   of  air 
passages,    195;    forms  of,  n; 
nerve,  245;    plain  muscle,  60; 
structure  of,  n 
Cellulose,  92,  141 
Cement  of  teeth,  114 
Centre  of  gravity  of  body,  68 
Centres,  nerve  (see  Nerve-cen- 
tres) 

Centres,  reflex,  use  of,  259 
Centrum  of  vertebrae,  23 
Cerebellum,  239;    functions  of, 

258 

Cerebral  hemispheres,  239 
Cerebro-spinal  liquid,  235 
Cerebrum,  256 
Cervical  enlargement  of  spinal 

cord,  236 

Cervical  vertebrae,  22 
Cheese,  nutritive  value  of,  97 
Chemical   changes    in   respired 

air,  209 

Chemical  composition  of  albu- 
mens, 15;  of  bile,  139;  of 
blood-serum,  154;  of  body, 
14;  of  bone.  42;  of  carbohy- 
drates, 16;  of  fats,  16;  of  gas- 
tric juice,  135;  of  lymph,  162; 
of  muscle,  61;  of  pancreatic 
secretion,  137;  of  red  cor- 


INDEX. 


puscles,  149;  of  respired  air, 
209 

Chest  (see  Thorax) 

Chondrin,  93 

Chordae  tendineae,  169 

Choroid,  269 

Chyle,  136,  141 

Chyme,  136 

Cilia,  195 

Circulation,  85,  176;  in  capilla- 
ries and  veins,  187;  portal, 
177;  pulmonary,  176;  sys- 
temic, 176;  diagram  of,  178 

Circulatory  organs,  163;  rela- 
tion of,  to  excretion,  86;  dia- 
gram of,  164 

Circulatory  system,  function  of 
the  different  parts  of  the,  163 

Circumduction,  49 

Circumvallate  papillae,  116 

Clavicle  (collar-bone),  20 

Clotting  of  blood  (see  Coagula- 
tion) 

Coagulation  of  blood,  152;  cause 
of,  152;  uses  of,  154 

Coccyx,  23 

Cochlea  280 

Coeliac  axis,  170 

Coffee,  99 

Cold,  exposure  to,  191 

Collar-bone  (clavicle),  20 

Colloids,  135,  146 

Colon,  126 

Colorless  blood  corpuscles,  150 

Comminuted  fracture  of  bones, 

44 
Common  bile-duct  (ductus  com- 

munis  choledochus,  129 
Compact  bone,  38;  structure  of, 

39 

Complemental  air,  199 
Compound  fracture  of  bone,  44 
Concha,  279 

Condiments  as  foods,  92 
Conductive  tissues,  296 
Connective  tissue,  18 
Conservation  of  energy,  law  of, 

74;  illustrations  of,  75 
Consonants,    classification    of, 

293 

Constructive  power  of  the  body, 
89 


Convolutions  of  the  brain,  240 
Cooking,  99 

Co-ordinating  tissues,  296 
Co-ordination,    231;  centre    of, 

258 
Cord,      spinal,      functions     of, 

254 

Corn,  nutritive  value  of,  98 
Cornea,  269 

Coronary  arteries,  168,  169 
Coronary  veins,  168 
Corpuscles  of  blood,  148 
Corti,  organ  of,  280 
Costal  cartilage,  28 
Costal  respiration,  206 
Cranial    nerves,  240;    sutures, 

29 

Cranium,  bones  of,  28 
Cricoid  cartilage,  291 
Crypts  of  Lieberkiihn,  125 
Crystalline  lens,  274 
Crystalloids,  146 
Cuticle  (epidermis),  220 

DEATH,  from  starvation,  78 

Death-stiffening  (rigor  mortis), 
59 

Defibrinated  blood,  153 

Deglutition  (see  Swallowing) 

Dentine,  114 

Dermal  senses,  283 

Dermis,  222;  papillae  of,  223 

Development  of  the  body,  295 

Dextrin,  94 

Diabetes,  300 

Dialysis  (osmosis),  145 

Diaphragm  (midriff),  8,  200 

Diarrhoea,  191 

Diastole  of  heart  beat,  iSo 

Diet,  advantages  of  a  mixed, 
101,  108;  relation  of  diet  to 
work,  104 

Dietaries,  standard,  104 

Differentiation  of  tissues,  296 

Digastric  muscle,  56 

Digestion,  84,  106;  gastric,  35; 
influence  of  saliva  in,  133;  in- 
testinal, iSr;  object  of,  131 

Diphtheria,  inoculation  in,  302 

Disassimilation,  86 

Disease  definition  of,  301;  im- 
munity from,  302 


INDEX. 


399 


Dislocations,   51;  reduction  of, 

51 

Division  of  labor,  physiologi- 
cal, 12 

Dorsal  (neural)  cavity,  5;  con- 
tents of,  5,  10 

Dorsal  vertebrae,  22 

Duct  of  glands,  109 

Duct,  common  bile,  129;  cystic, 
129;  hepatic,  128;  of  parotid 
gland,  119;  of  submaxillary 
gland,  119 

Duodenum,  123,  130 

Dura  mater,  235 

Dyspepsia,  142 

EAR,  329 

Efferent    (motor)    nerves,    250, 

252 

Egg-albumin,  15,  93 
Eggs,  nutritive  value  of,  97 
Eighth   pair   cranial  (auditory) 

nerves,  242 
Elasticity   of  the  arteries,  188, 

189;  of  the  lungs,  198 
Elastic  tissue,  141 
Elbow  joint,  50,  55 
Elements  found  in  the  t>ody,  14 

(foot-note) 
Eleventh    pair    cranial   (spinal 

accessory)  nerves,  242 
Emmetropic  eye,  276 
Emulsion,  138 
Enamel,  114 
Endolymph,  280 
Endoskeleton,  17  (foot-note) 
Energy,  74,  80;  chief  forms  of, 

expended    by    the    body,    80; 

conservation  of,  74,  80;  source 

of,  in  the  body,  76 
Epidermis,  220 
Epiglottis,  120,  290 
Equilibrium,   nitrogenous,  94 
Equilibrium,  sense  of,  282 
Ethmoid  bone,  29 
Eustachian  tube,  120,  279 
Excretion  and  reception,  inter- 
mediate steps  between,  84 
Excretions,  removal  of,  86 
Excretory  organs,  84 
Exercise,  72;  effect  of,  298 
Exoskeleton,  17  (foot-note) 


Expiration,  198,  203 

Extension  at  joints,  49 

Extensor  muscles,  64 

External  auditory  meatus,  279 

External  ear,  279 

Extracts  of  meat,  63 

Eye,  accommodation  of,  globe 
of,  269;  hygiene  of,  277;  re- 
fracting substances  of,  274 

Eyeball,  anatomy  of,  269 

Eyelashes,  267 

Eyelids,  266 

Eye-socket,  266 

FACE,  bones  of,  29 

Facial  nerve,  242 

Fasciculi  of  muscles,  58 

Fats  (hydrocarbons),  16,  94;  ab- 
sorption of,  190;  action  of 
bile  on,  134;  of  gastric  juice 
on,  135;  of  pancreatic  secre- 
tion on,  138;  as  a  reserve 
food,  78,  81;  emulsifying  of 
138,  141 ;  kinds  of,  in  body,  16 

Fatty  acids,  94 

Fauces,  119;  isthmus  of  the, 
no,  134;  pillars  of  the,  119 

Femoral  artery,  170 

Femur,  21,  47 

Fibres,  u;  plain  muscle,  59; 
striped  muscle,  58;  nerve, 

243 

Fibrillae,  59 

Fibrin,  16,   153 

Fibrinogen,  91,  153 

Fib'ula  (peroneal  bone),  21,  39 

Fifth  pair  cranial  (trigeminal) 
nerves,  241 

Filiform  papillae,  117 

Flatulence,  122 

Flexion  at  joints,  49 

Flexor  muscles,  64 

Food,  accessory,  92;  amount  of, 
required  daily,  100;  analyses, 
103  ;  as  a  force  generator, 
91;  as  a  force  regulator,  91; 
as  a  machinery  former,  91; 
as  a  tissue  former,  88;  com- 
position of,  88;  cooking  of, 
99;  inorganic,  95;  alcohol  as  a 
food,  98;  need  of,  76,  77;  non- 
oxidizable,  90;  nutritive  val- 


400 


INDEX. 


ue  of  different,  96;  necessity 
of  proteid,  93;  special  impor- 
tance of  albuminous,  89;  sup- 
ply of  animal,  90 
Food  principles,  fuel  values  of, 

95 

Foodstuffs  (see  Alimentary 
principles) 

Foot,  skeleton  of,  22;  peculiari- 
ties of  human,  35 

Foramen,  intervertebral,  24; 
magnum,  28,  234;  oval,  280 

Force-generating  foods,  91 

Force-regulating  foods,  91 

Forearm,  movements  of,  50,  55 

Fore-limb  (see  Upper-limb) 

Fossa,  glenoid,  49 

Fourth  pair  cranial  (pathetici) 
nerves,  240 

Fractures  of  bones,  44 

Free  (floating)  ribs,  28 

Frog's   web,  circulation  in,  187 

Frontal  bone,  28 

Fruits,  nutritive  value  of,  98 

Fuel  values  of  food  principles, 

95 

Fundamental  tone,  282 
Fungiform  papillae,  116 
Furred  tongue,  117 

GALL  (see  Bile) 
Gall  bladder,  129 
Games,  use  of,  73 
Ganglia,   234,    255  ;    Gasserian, 
241;  spinal,  238;  sympathetic, 

243 

Gases  of  the  blood,  155 

Gasserian  ganglion,  241 

Gastric  digestion,  135 

Gastric  glands,  121 

Gastric  juice,  121,  135 

Gelatine    42,  93 

Gelatinization,  stage  of,  in  co- 
agulation, 152 

Giantism,  300 

Glands,  106;  forms  of,  109;  gas- 
tric, 121 ;  internal  secretion 
of,  299:  kinds  of,  107;  lachry- 
mal, 107;  lymph,  161;  mam- 
mary, 8;  Meibomian,  267;  of 
skin,  220;  of  small  intestine, 
125;  salivary,  119 


Glenoid  fossa,  49 
Gliding  joints  (arthrodia),  51 
Glosso-pharyngeal  nerves,  242 
Glottis,  288 

Glucose  (grape    sugar),  16,   94; 
conversion  of  starch  into,  132 
Gluten,  93,  97 
Glycerine,  16,  94 
Glycocholic  acid,  139 
Glycogen,  16,  95,  130,  144 
Grape  sugar  (see  Glucose) 
Gray  nerve  fibres,  245 
Gullet  (see  CEsophagus) 
Gums,  94,  112 

HABITS,  260 

Haemal  cavity  (see  Ventral  cav- 
ity) 

Haemoglobin,  150,  179,  214 

Hair-follicle,  235 

Hairs,  225 

Hand,  skeleton  of,  21 

Hard  palate,  TII 

Haversian  canals,  40 

Haversian  system,  41 

Health,  definition  of,  301 

Hearing,  279 

Heart,  7;  beat  of,  180;  cavities 
of,  166;  dissection  of,  178; 
position  of,  165;  how  nour- 
ished, 167;  muscle  of,  61; 
nerves  of,  185;  palpitation  of, 
122;  sounds  of,  183;  vessels 
connected  with,  166;  work 
done  by  daily,  184 

Heat  of  body,  source  of,  76;  in- 
fluence of  starvation  upon, 

77 

Heat  units,  95 

Hepatic  artery,  128 

Hepatic  duct,  128 

Hepatic  veins,  177 

Hibernation,  78  (foot-note) 

High  heels,  bad  effects  of,  43 

Hilus  of  kidney,  217 

Hind  limb  (see  Lower  limb) 

Hinge  joints  (ginglymi),  49 

Hip-joint,  21,  46 

Histology,  definition  of,  2;  of 
blood,  148;  of  bone,  40;  of 
kidneys,  218;  of  lungs,  197;  of 
lymph,  161;  of  muscle,  58;  of 


INDEX. 


461 


nerve  cells,  245;  of  nerve 
fibres,  244;  of  retina,  270;  of 
skin,  220 

Hollow  veins  (see  Venae  cavae) 
Human  anatomy,  definition  of, 

i,  8,  12 
Human    physiology,   definition 

of,  i,  2,  12 
Humerus,  21,  36 
Hunger,  264 

Hydrocarbons  (see  Fats) 
Hydrochloric  acid,  15,  135 
Hygiene,   definition  of,  i,  2;  of 
blood,  156;  of  bony  skeleton, 
43;  of  brain,  261;  of  eyes,  277; 
of  muscles,  71;  of  respiration, 
205;  of  skin,  227;  of  teeth,  114 
Hyoid  bone,  20,  115 
Hypermetropia,  276 
Hypermetropic  eye,  276 
Hypoglossal  nerves,  243 

ILEO-CCECAL  valve,  127 

Ileum,  123 

Iliac  arteries,  170 

Immunity  from  disease,  302 

Impulse,  nature  of  nervous,  247 

Incisors,  112 

Incus  (anvil  bone),  280 

Indigestible  substances,  141 

Infection,  resistance  of  body  to, 

151 

Inferior  maxillary  bone  (mandi- 
ble), 29 

Inferior  maxillary  nerve,  242 

Inferor  turbinate  bone,  29 

Innominate  artery,  169 

Innominate  bone  (os  innomina- 
tum  or  pelvic  bone),  21,  47 

Inoculation  in  diphtheria,  302 

Inorganic  constituents  of  the 
body,  15 

Inorganic  foods,  95 

Insertion  of  muscles,  55 

Inspiration,  198,  203 

Intercellular  substance,  12,  17 

Intercentral  fibres,  258 

Internal  ear  (labyrinth),  279,  280 

Internal  secretion  of  glands, 
299 

Intervertebral  foramina,  24; 
disks,  25 


Intestinal  digestion,  141 

Intestinal  juice  (succus  enteri- 
cus),  140 

Intestines,  digestion  in,  141; 
large,  125  (see  Large  intes- 
tine); small,  123  (see  Small 
intestine) 

Invertebrate  animals,  charac- 
teristics of,  6 

Invertin,  131 

Involuntary  muscles,  60 

Iris,  269,  273 

Irritable  tissues,  296 

Isthmus  of  the  fauces,  no, 
134 

JEJUNUM,  123 

Joint,  ankle,  22;  elbow,  50,  55; 
hip,  21,  47;  knee,  49,  shoul- 
der, 32,  49 

Joints,  19;  ball  and  socket,  48; 
general  structure  of,  46;  glid- 
ing, 51;  hinge,  49;  pivot,  50; 
movements  at,  44 

KIDNEYS,  7,  215,  300;  gross  an- 
atomy of,  217;  histology  of, 
218;  secretion  of,  219 

Knee-cap  (patella)  21 

Knee-joint,  49 

LABOR,  physiological  division 
of,  12 

Labyrinth  (internal  ear),  280 

Lachrymal  apparatus,  267 

Lachrymal  bones,  29 

Lachrymal  glands,  107 

Lacteals,  124,  145,  161 

Lactose  (milk  sugar),  16,  95 

Lacunae  of  bone,  41 

Lamellae  of  bone,  41 

Large  intestine,  in,  125;  ab- 
sorption from,  146 

Larynx,  195,  289;  muscles  of, 
291 

Leg,  skeleton  of,  21 

Levers  in  the  body,  64 

Lieberkiihn,  crypts  of,  125 

Liebig's  extract  of  meat,  63 

Ligaments,  18,  47;  capsular,  47; 
round,  47;  transverse,  of 
atlas,  24,  50 


462 


•INDEX. 


Light,  action  of,  on  the  retina, 

.273 

Limbs,  comparison  of  upper 
and  lower,  29;  general  struc- 
ture of,  8 

Liver,  127;  functions  of,  130 

Localization  of  sensations  of 
brain,  257 

Locomotion,  69 

Long  bones,  39 

Long     sight    (hypermetropia), 

275 

Lower  jaw,  bone  of,  29;  move- 
ments of,  49 

Lower  limb,  comparison  of  up- 
per and,  29;  peculiarities  of, 
in  man,  34;  skeleton  of,  21 

Lumbar  enlargement  of  spinal 
cord,  236 

Lumbar  vertebrae,  22 

Lungs,  6,  84,  196;  changes  un- 
dergone by  blood  in,  214; 
elasticity  of,  198;  quantity  of 
CO2  passed  out  from,  in  a 
day,  210;  quantity  of  O  taken 
up  by,  in  a  day,  210;  renewal 
of  air  in,  198;  why  they  fill 
with  air,  204 

Lunula  of  nails,  225 

Lymph,  157;  chemistry  of,  162; 
histology  of  161;  renewal  of, 
158 

Lymphatics  of  small  intestine, 
124 

Lymphatic  vessels  (absorbents), 

159 

MAGNESIUM  phosphate,  96 

Malar  bone,  29 

Malleus    (hammer)  bone,  280 

Malpighi,  pyramids  of,  217 

Maltose,  132 

Mammalia,  definition  of,  8,  10 

Mammary  glands,  8 

Man,  as  a  vertebrate  animal,  5, 
10;  place  of,  among  verte- 
brates, 8,  10 

Mandible  (inferior  maxillary 
bone>,  29 

Margarin,  94 

Marrow,  38,  3g;red,  38;  yellow, 

39 


Matrix,  225 

Maxilla      (superior      maxillary 

bone),  29 
Maxillary  nerve,   inferior,    242; 

superior,  242 
Meat  extracts,  63 
Meats,  cooking  of,  99;  nutritive 

value  of,  97 

Medulla  oblongata,  240,  255 
Medullary    cavity  of  bone,  38, 

40 
Medullary    sheath    of    nerves, 

245 

Meibomian  follicles,  267 

Membranes  of  the  brain  and 
spinal  cord,  234 

Mesenteric  arteries,  170 

Metacarpal  bones,  21,  39 

Metatarsal  bones,  22,  39 

Microscopic  anatomy  (see  His- 
tology) 

Middle  ear,  279 

Midriff  (see  Diaphragm) 

Milk,  as  a  food,  44;  nutritive 
value  of,  97;  sugar  (lactose), 
16,  95;  teeth,  112 

Mitral  valve,  169 

Molar  teeth,  112 

Motor  (efferent)  nerves,  250, 
252 

Motor  stimuli,  218 

Motor  tissues,  296 

Mouth  cavity,  no,  in;  absorp- 
tion from,  144 

Movements,  at  joints,  49;  of 
eyeball,  268;  of  the  body,  how 
effected,  46;  in  space,  69 

Mucin,  141 

Mucous  coat,  small  intestine, 
123 

Mucous  membrane,  of  air-pas- 
sages, 195;  of  alimentary 
canal,  106 

Mumps,  119 

Muscles,  46,  52;  chemical  com- 
position of,  61;  contraction 
of,  54;  gross  structure  of,  57; 
histology  of,  58;  how  con- 
trolled, 56;  hygiene  of,  71;  of 
arteries,  190;  of  heart,  61;  of 
larynx,  291;  of  small  intes- 
tine, 125;  of  stomach,  123; 


MDEX. 


403 


origin  and  insertion  of,  55; 
papillary,  169,  181;  parts  of, 
52;rectus  abdominis,  56;  spe- 
cial physiology  of,  64;  varie- 
ties of,  55 

Muscular  fibres,  58 

Muscular  sense,  285 

Muscular  tissue,  striped,  57; 
plain,  59 

Muscular  work,  influence  of 
starvation  upon,  77;  source, 

74 

Musculo-motor  nerves,  252 
Mustard,  use  of,  as  a  food,  92 
Myopia,  276 
Myopic  eye,  276 
Myosin,  16,  61,  93 

NAILS,  225 

Nares,  posterior,  29 

Nasal  bones,  29 

Nerve  action,  248 

Nerves,  cranial,  240;  kinds  of, 
243;  spinal,  237 

Nerves,  heart,  185;  inferior 
maxillary,  242;  ophthalmic, 
241;  superior  maxillary,  242; 
sympathetic,  243;  trophic,  297 

Nerve-cells,  245 

Nerve-centres,  232,  234,  246 

Nerve-fibres,  afferent  and  effer- 
ent. 250;  kinds  of,  243 

Nerve-ganglia,  234 

Nerve-trunks,  232 

Nervous  control  of  respiration, 
205 

Nervous  impulses,  nature  of, 
247 

Nervous  system,  anatomy  of, 
230 

Neural  arch,  24 

Neural  cavity  (see  Dorsal  cav- 
ity) 

Neurilemma  of  nerve  fibre,   244 

Neuron  of  axis  cylinder,  245, 
248 

Ninth  pair  cranial  (glosso-pha- 

ryngeal)  nerves,  242 
Nitrogen-excreting     organs, 

general  arrangement  of,  215 
Nitrogenous  equilibrium,  94 
Non-oxidizable  foods,  90 


Non-vascular  tissues,  148 
Nucleolus,  ii 
Nucleus,  ii 

Nutrition,  86;  of  cells,  297 
Nutritive  tissues,  296 
Nutritive     value     of     differen 
foods,  96 

OCCIPITAL  bones,  28 

Odontoid  (tooth-like)  process  of 
the  axis,  29,  50 

Odorous  substances,  286 

(Esophagus (gullet),  6,  no,  120; 
absorption  from,  144 

Oil  glands  (sebaceous  glands), 
227 

Oils  (see  Fats) 

Oleic  acid,  16 

Oleine,  16,  94 

Olfactory  lobes,  239 

Olfactory  nerves,  240 

Ophthalmic  nerves,  241 

Optic  commissures,  240 

Optic  nerves,  240,  265 

Organ,  definition  of,  3;  circula- 
tory, 85,  163,  164;  digestive, 
85,  106;  nitrogen-excreting, 
215;  of  hearing,  279;  of  sight, 
265,  of  smell,  286;  of  taste, 
286;  of  temperature  sense, 
283;  of  touch,  283;  receptive 
and  excretory,  84;  respira- 
tory, 85,  193 

Organ  of  Corti,  280 

Organic  constituents  of  the 
body,  15 

Organic  matter,  relation  of,  to 
carbon  dioxide  determined 
by  odor,  213 

Origin  and  insertion  of  muscles, 
55 

Os  innominatum  (see  Innomi- 
nate bone) 

Osmosis,  145 

Oval  foramen,  280 

Overtones,  282 

Oxidations,  78,  79 

Oxidations  in  the  body,  78 

Oxygen  absorption  of,  from  the 
lungs,  179  214;  in  the  blood, 
155;  influence  of,  on  the  color 
of  the  blood,  214;  quantity 


404 


INDEX. 


of,  taken  up  by  the  lungs  in  a 

day,  210 

Oxygen  food  of  the  body,  81 
Oxyhaemoglobin,  179,  214 

PAIN,  sensations  of,  249,  285 

Palate,  in 

Palate  bones,  29 

Palmatin,  16,  94 

Palmitic  acid,  16 

Palpitation  of  the  heart,  122 

Pancreas,  128,  130,  300 

Pancreatic  secretion,  137;  ac- 
tion of,  on  foodstuffs,  138 

Papillae  of  the  dermis,  223 

Papillae  of  the  tongue,  116 

Papillary  muscles,  169;  use  of 
the,  181 

Parietal  bones,  28 

Parotid  gland,  119 

Patella  (knee-cap),  21 

Peas,  nutritive  value  of,  98 

Pectoral  arch  or  girdle,  20; 
comparison  of  pectoral  and 
pelvic  girdles,  30 

Pedicle  of  vertebrae,  24 

Pelvic  arch  or  girdle,  21;  com- 
parison of  pectoral  and  pel- 
vic girdles,  32 

Pelvis,  21,  34 

Pelvis  of  kidney,  217 

Penniform  muscles,  56 

Pepper,  use  of,  as  a  food,  92 

Pepsin,  131,  135 

Peptones,    135;    absorption  of, 

144 

Pericarditis,  165 
Pericardium,  165 
Perilymph,  280 
Perimysium,  58 
Periosteum,  36,  39 
Peristalsis,  125 
Peritoneum,  109 
Permanent  teeth,  112 
Peroneal  artery,  170 
Perspiration,  226 
Phagocytosis,  151 
Phalanges  of  fingers,  21,  39;  of 

toes,  22,  39 
Pharynx,    no,   119;  absorption 

from,  144 
Phosphate  of  lime,  15,  43,  44 


Physiological  division  of  labor, 

12 
Physiology,    human,   definition 

of,  i,  2,  12 
Physiology   of  muscle,   special 

and  general,  64 
Pia  mater,  235 
Pillars  of  the  fauces,  119 
Pitch,  282,  288 
Pituitary  body,  300 
Pivot  joints,  50 
Plain  muscular  tissue,  59 
Plants,  as  food  for  animals.  90 
Pleura,  197 
Pleurisy,  187 

Pneumogastric  nerves,  185,  242 
Poison,  definition  of,  92 
Polygastric  muscles,  56 
Pons  Varolii,  239 
Popliteal  artery,  170 
Pork,  nutritive  value  of,  97 
Portal  circulation,  177 
Portal  vein,  128,  177 
Posterior  nares,  29 
Potassium  phosphate,  96 
Potatoes,  nutritive  value  of,  98 
Premolars  (bicuspids),  112 
Presbyopia,  278 

Primitive  sheath  of  nerves,  244 
Pronation,  50 
Protective  tissues,  296 
Proteid   alimentary   principles, 

93 

Proteid  food,  necessity  of,  93 

Proteid  substances  (see  Albu- 
minous substances) 

Ptomaines,  301 

Ptyalin,  131 

Pulleys  in  the  body,  67 

Pulmonary  artery,  167 

Pulmonary  circulation,  163,  176 

Pulmonary  veins,  167 

Pulp  cavity  of  tooth,  113 

Pulse,  186  ;  disappearance  of, 
in  capillaries  and  veins,  189  ; 
hard  and  soft,  186  ;  rate  of, 
1 86 

Pupil,  270,  273 

Pus,  152 

Pyloric  orifice  of  stomach,  121 

Pyloric  sphincter,  122 

Pyramids  of  Malpighi,  217 


INDEX. 


4°  5 


RACEMOSE  (acinous)  glands,  107, 
109 

Radial  artery,  170,  186 

Radius,  21,  39 

Reaction,  modes  of  nervous, 
258  ;  voluntary,  254 

Reception  and  excretion,  inter- 
mediate steps  between,  84 

Receptive  organs  of  the  body, 
84 

Rectum,  126 

Rectus  abdominis  muscle,  56 

Red  blood  corpuscles,  composi- 
tion of,  155;  function  of,  150; 
of  man,  149  ;  of  other  ani- 
mals, 150 

Red  marrow,  38 

Reducing  dislocations,  51 

Reflex  action,  251  ;  spinal,  254 

Reflex     centres,    259  ;    use     of, 

259 

Refracting  media  of  the  eye, 
269,  274 

Renal  arteries,  170,  215,  218 

Renal  secretion  (urine),  219 

Renal  veins,  215 

Rennin,  131 

Reproductive  tissues,  88 

Residual  air,  199 

Resonance,  289 

Respiration,  85;  abdominal,  206; 
chemistry  of,  209;  costal,  206; 
hygiene  of,  205,  212;  nervous 
control  of,  205;  object  of,  193 

Respiratory  centre,  205 

Respiratory  organs,  85,  194  ; 
anatomy  of,  193 

Respiratory  sounds  or  mur- 
murs, 203 

Retina,  265;  histology  of,  270 

Ribs,  20,  28;  action  of,  in  respi- 
ration, 201 

Rice,  nutritive  value  of,  98 

Rotation  at  joints,  49 

Round  ligament,  47 

Running,  71 

SACRUM,  23,  25 

Saliva,  131;  chemical  action  of, 

132;  influence  of,  in  digestion, 

133;  uses  of,  132 
Salivary  glands,  119 


Salt,  as  a  constituent  of  the 
body,  15  ;  importance  of,  as 
food,  96 

Saponification,  138 

Sarcolemma,  58 

Scapula  (shoulder-blade),  20,  39 

Sclerotic,  269 

Scurvy,  98 

Sebaceous  glands  (oil  glands), 
227 

Sebaceous  secretion,  227 

Secretion,  internal,  of  glands, 
109;  of  gastric  glands,  122, 
J35  I  °f  glands  of  small  intes- 
tine, 140;  of  kidneys,  219;  of 
lachrymal  gland,  267  ;  of 
liver,  128,  139  (see  Bile);  of 
Meibomian  follicles,  267  ;  of 
pancreas,  137  (see  Pancreatic 
secretion);  of  salivary  glands, 
131  (see  Saliva);  of  sebaceous 
glands,  227;  of  sweat  glands, 
226 

Secreto-motor  nerves,  252 

Segmentation,  295 

Semicircular  canals,  280 

Semilunar  valves,  168,  181,  282; 
demonstration  of  action  of, 

Semivowels,  293 

Sensation  and  motion,  relation 
between,  253 

Sensations,  248;  common,  264; 
localization  of  skin,  284 

Sense,  muscular,  285 

Senses,  special,  263;  common, 
264;  dermal,  283 

Sensory  (afferent)  nerves,  250 

Sensory  stimuli,  249 

Septum  of  heart,  166 

Serous  membrane,  165 

Serum  (see  Blood-serum) 

Serum  albumin,  15;  coagula- 
tion of,  155 

Seventh  pair  cranial  (facial) 
nerves,  242 

Shaft  of  bones,  38 

Short  bones,  39 

Short  sight  (myopia),  275 

Shoulder  girdle  (see  Pectoral 
arch) 

Shoulder  joint,  32,  49 

Shower  baths,  229 


406 


INDEX. 


Sight,  sensation  of,  265;  organ 
of,  265 

Sigmoid  flexure,  127 

Simple  fracture  of  bones,  44 

Sixth  pair  cranial  (abducentes) 
nerves,  242 

Skeleton,  appendicular,  20;  axi- 
al, 20;  composition  of,  17;  of 
cranium,  28;  of  face,  29;  of 
lower  limb,  21;  of  upper 
limb,  21;  peculiarities  of 
human,  33 

Skin,  220;  as  a  sense-organ, 
227;  glands  of,  226;  histology 
of,  220;  hygiene  of,  227 

Skull,  20,  28;  peculiarities  in 
the  position  of,  33 

Sleep,  156 

Small  intestine,  in,  123;  ab- 
sorption from,  144;  glands 
of,  125;  lymphatics  of,  124; 
mucous  coat  of,  123;  muscu- 
lar coat  of,  125;  villi  of, 
124 

Smell,  286 

Soft  palate,  in 

Sound,  282 

Sounds  of  the  heart,  183 

Sounds,  respiratory,  203 

Sound  waves,  action  of,  on  the 
ear,  280 

Special  physiology  of  muscles, 
64 

Speech,  289 

Sphenoid  bone,  29 

Spinal  accessory  nerves,  242 

Spinal  cord,  7,  235;  functions 
of,  254 

Spinal  ganglia,  243 

Spinal  nerves,  237 

Spinal  reflex,  254 

Spine  (see  Vertebral  column) 

Spinous  process  of  vertebrae 
(neural  spine),  24 

Spleen,  163,  299 

Spongy  (cancellated)  bone,  38 

Sprains,  51 

Standing,  67 

Stapes  (stirrup  bone),  280 

Starch,  99;  action  of  bile  on, 
139;  of  gastric  juice  on,  136; 
of  pancreatic  secretion  on, 


137;  of  saliva  on,  133;  solu- 
ble, TOO 

Starvation,  death  from,  78;  in- 
fluence of,  on  muscular  work 
and  animal  heat,  77 

Steapsin,  131,  138 

Stearic  acid,  16 

Stearin,  16,  94 

Sternum  (breast-bone),  20 

Stimulants,  92 

Stomach,  6,  no,  121;  absorp- 
tion from,  144;  digestion  in, 
r35J  glands  of,  121 ;  musculai 
coat  of,  122 

Storage  tissues,  296 

Striped  muscular  tissue,  57,  58 

Sub-clavian  artery,  169 

Sub-lingual  gland,  119 

Sub-maxillary  gland,  119 

Suffocation,  82,  210 

Sugar,  cane,  95;  grape  (see 
Grape  sugar) 

Sugar  of  milk  (lactose),  16,  95 

Superior  maxillary  bone,  29 

Superior  maxillary  nerve,  242 

Supination,  50 

Supplemental  air,  199 

Supporting  tissues,  296 

Suprarenal  capsule 

Swallowing    (deglutition),    120, 

133 

Sweat,  226 
Sweat    (sudoriparous)    glands, 

109,   226 

Sweetbread  (see  Pancreas) 
Sympathetic    nerve   centres,   7, 

10,  243;  ganglia  of,  243 
Synovial  fluid,  48 
Synovial  membrane,  48 
Syntonin,  61,  93 
Systemic  circulation,  163,  176 
Systole  of  heart-beat,  180 

TABULAR  bones,  39 

Tarsal  bones,  22,  39;  joints  be- 
tween, 51 

Tarsus,  benefits  of  peculiar 
structure  of,  35 

Taste,  286 

Taurocholic  acid,  139 

Tea,  99 

Tears,  267 


INDEX. 


407 


Teeth,  characteristics  of  indi- 
vidual, 112;  general  structure 
of,  113;  hygiene  of,  114;  kinds 
of,  113 

Temperature  changes  in  re- 
spired air,  209 

Temperature  of  the  body,  76; 
regulation  of,  77;  regulation 
by  means  of  sweat  glands, 
226  (foot-note) 

Temperature  sense,  283 

Temporal  artery,  186 

Temporal  bone,  28 

Tendons,  18,  52,  53 

Tenth  pair  cranial  (pneumogas- 
tric)  nerves,  242 

Thein,  92 

Thigh  bone  (femur),  21 

Third  pair  cranial  (motores 
oculi)  nerves,  242 

Thirst,  264 

Thoracic  aorta,  170 

Thoracic  duct,  161 

Thorax,  contents  of,  8;  dorso- 
ventral  enlargement  of,  201; 
structure  of,  200;  vertical  en- 
largement of,  200 

Thyroid  cartilage,  290 

Thyroid  glands,  299,  300 

Tibia,  21,  39 

Tibial  artery,  170 

Tidal  air,  199 

Tight  lacing,  evil  effects  of, 
206 

Timbre,  282 

Tissues,  classification  of,  3 
(foot-note);  connective,  18; 
differentiation  of,  296;  nerve, 
243;  non-vascular,  148;  plain 
muscular,  59;  striped  muscu- 
lar, 57;  subcutaneous  areolar, 
222;  ultimate  structure  of,  II 

Tone,  282;  fundamental,  282 

Tongue,  115;  furred,  117 

Tonsils,  119 

Touch,  283 

Toxin,  302 

Trachea  (windpipe),  6,  195; 
structure  of,  195 

Transverse  ligament  of  the  at- 
las, 25,  50 
Triceps  muscle,  56 


Triceps  muscles,  definition  of, 

55 

Trichina,  97 
Tricuspid  valve,  169 
Trigeminal  nerves,  241 
Trophic  nerves,  252,  297 
Trypsin,  137 
Tubular  glands,  107,  109 
Turbinate  bones,  29 
Turnips,  nutritive  value  of,  98 
Twelfth  pair  cranial  (hypoglos- 

sal)  nerves,  243 
Tympanic  membrane,  279 

ULNA,  21,  39 

Ulnar  artery,  170 

Undifferentiated  tissues,  118 

Units,  heat,  118 

Unstriped  muscle  cells,  60 

Upper  jaw  bone,  29 

Upper  limb,  comparison  of  up- 
per and  lower  limbs,  29;  skel- 
ton  of,  21 

Urea,  83,  219;   useless  as  food 
96 

Ureters,  215 

Urethra,  215 

Urinary  bladder,  215 

Urine,  219 

Uriniferous  tubules,  219 

Uvula,  112 

VACCINIA  (cowpox),  303 

Vagi,  242 

Valves,     auriculo -ventricular, 

169,  181;   ileo-ccecal,  127;   of 

the  veins,  I74;semilunar,  169, 

181 

Valvulae  conniventes,  123 
Vaso-motor  nerves,  252 
Veins,     164,     173;   absence    of 

pulse  in,  189:   circulation  in, 

186;  valves  of  the,  177 
Veins,   coronary,  168;   hepatic, 

177;  hollow  (venae  cavae),  166; 

portal,  128,  177;  pulmonary, 

167;  renal,  215 
Vegetable  casein,  93 
Venae  cavae  (hollow  veins),  166 
Venous  blood,  150,  179 
Ventilation,  210;    methods   of, 

213 


4o8 


INDEX. 


Ventral  (haemal)  cavity,  5;  con- 
tents of,  5,  7,  10 
Ventricles,.  166 
Ventricular  contraction,  181 
Vermiform  appendix,  126 
Vertebrae,   23,  34;  structure  of, 

23 

Vertebral  column  (spine,  back- 
bone), 5,  20,  22,  27;curvatures 
of,  25;  mechanism  of,  25;  pe- 
culiarities of  human,  34 

Vertebrate  animals,  character- 
istics of,  6;  classification  of,  8 
(foot-note) 

Vestibule  of  ear,  280 

Villi  of  small  intestine,  124 

Viscero-motor  nerves,  252 

Visual  apparatus,  265 

Visual  centre,  265 

Vital  capacity,  199 

Vitreous  humor,  270 

Vocal  cords,  288,  291 

Voice,  288;  range  of  human, 
291 

Voluntary  muscles,  59  (see  also 
foot-note) 

Voluntary  reaction,  254 

Vomer,  29 


Vowels,  293 

WALKING,  69 

Warm  baths,  229 

Wastes  of  the  body,  83;  removal 
of,  141,  148 

Water,  as  a  constituent  of  the 
body,  15;  as  a  food,  90,  95; 
as  a  force  regulator,  91;  as  a 
waste  product,  83;  quantity 
of,  lost  through  the  kidneys, 
219;  through  the  lungs,  209; 
through  the  skin,  227 

Wheat,  nutritive  value  of,  97 

Whipped    (defibrinated)    blood» 

153 

White  blood  corpuscles,  150 

White  nerve  fibres,  244 

Windpipe  (see  Trachea) 

Wisdom  teeth,  112 

Woollen  garments,  191 

Work,  daily,  of  heart,  184;  esti- 
mates of  daily  mechanical, 
104;  influence  of  starvation 
upon  muscular,  77;  power  of 
the  body  to  do,  74;  relation  oi 
diet  to,  104 


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